CHAPTER XIX.
On the Reproductive Organs of Acotyledonous plants.
17th.—Fine weather, the sun daily increasing in power, is having a remarkable effect on the peculiar spring vegetation, but this is not sufficiently developed to bring in the corresponding birds and insects. Gypaëtos is common now about the dead camels.
On the low east ridge, along the path that leads over the river, ruins of ancient times are discernible, this only adds another to the many proofs of similarly situated ruins, that the people who built them have been located about Cabul, Jallalabad, and Peshawur, certainly not about Candahar.
In the soil between the rocks, and in their crevices saturated with moisture, most of the plants are just sprouting. Trichonema, Crocus, and one or two other monocotyledons, Labiatæ? Sedum three or four species, exclusive of Sedoides foliis deltoides sphathulatis, and a Stapelioid Asclepias, are to be found. I also got a new fern, the fourth species out of 1,300 sp. it is a Ceterach or Grammitis, a curious stalked snuff-ball, and one or two other Fungi, with an inverted cap, were met with.
In the fields a young Ranunculus in profusion, Veronica agrestis, Euphorbia, Festuca annua?
Kochia spinosa, and a curious Mathioloid are among the few wild plants to be found about Pushut.
It would be a curious circumstance if all indusiate ferns were to be found reducible to a marginal production of the reproductive apparatus. I will bear this in mind, as certain forms of Pteris or its affinities lead me to suspect that in these tribes the indusium may be a long way from the margin, and yet be, quoad origin, marginal; this section illustrates my meaning.
The transition to this might reasonably be suspected. The philosophy of ferns is most ill understood, the higher points connected with them have been quite neglected, and botanists in this as in other departments of the science have been contented to confer names on certain external forms, without sufficient regard to structure.
To-day I commenced examining Adiantum, with the view of determining if possible the nature of its reproductive organs, and the mode in which they are impregnated, if they are impregnated at all.
As I had long been aware that the fructification of each frond is a thing to be determined at a very early period, and that if not determined then, it is never likely to be determined afterwards, my attention was directed more strongly, if possible, than it would have been otherwise, to examining the subject at the earliest possible stage of its development.
The first piece examined gave me the idea that I had trouvé le nœud de l’affairé; the second made me doubt this; the subsequent ones went far to disprove it.
I was immediately struck with the resemblance of those organs, called ramenta, to what are fairly assumed to be the male bodies, in certain other families of the same grand division; and I at once came to the conclusion, that the barren fronds, were barren, because almost destitute of these ramenta; and that as these ramenta were confined to the base of the stalk, that is, to the part below its first ramification, an obvious necessity existed for the peculiar nature of the vernation.
Further examination of the thing, especially of the base of the stipes and the adjoining part of the rhizoma, threw me back almost into my original difficulties. I find that the rhizoma is entirely covered with ramenta, which are brown, much detached at the base, and obviously represent a low form of leaf, i.e. in appearance, perhaps partly in function, but not in structure. Among these, mature ramenta at the punctas of prolongation, which appear to be very irregular, are concealed, others much smaller, and much narrower, (which bear as obvious a resemblance, or even more so to the male organs of certain other orders,) than the ramenta on the stipes. These are never entirely brown, the end cell alone is coloured, but though occasionally tinged with brown, they are filled with some fluid (even this is not so at first,) but do not appear to open. I believe that subsequently all become highly tinged with brown, but what increase of growth they subsequently undergo, I know not. The terminal cell is always solitary, very often attached to the one next it, which is generally single, obliquely placed, occasionally looking like the dimidiate calyptra capping a young seta. The number of cells forming the base, or dilated part varies, but is always small in proportion to the larger ramenta, or protecting scales: these last have a single terminal cell, which in fact must be the same in every really cellular growth sooner or later, the last degree of formative power being the production of a single cell.
At a subsequent period, still an early one, the terminal cell is fuscous-brown, and this colour then extends to the next in various degrees, but if it reaches the basilar ones at all, it does so at late periods. The base of the terminal cell, and parts of the parietes of the next and next, present a coagulated appearance, precisely as in certain mosses.
No such thing as a petiolate leaf occurs in acrogens, all are attached by a broad base? Of acrogenous leaves, those only are leaves whose attachment is at right angles with the stem; the rest are divisions of a frond. Thus far with the ramenta. The divisions of the frond, are, I find, not gyrate, but rather cochleariform involate. The future reproductiveness is settled at a very early period, and is distinguishable under the microscope by a sort of margination of the frondlets. In the earliest stage I have looked at, the margin is greenish, striated by narrow cells, and passes into the body of the leaf gradually; the greater development is perhaps central; even now the bulk of the cells of the leaflet have green granules, and are opaque from air. The vessels are marked out, or at least their future course, and along them the opacity from air does not exist, so that the veins appear depressed.
The next stage presented a greater development of an isolation of the margin, but no other change. The next presented an isolation of the margin, which remains almost white, the other part being green, but more so because of a thickening as it were along the base of the marginal part, and an evident deposit of grumous matter, from which, under every circumstance new tissue seems always to be developed. Pressure causes its discharge, its contents were unappreciated by my poor instruments; after this the leaflets revert to the appearance of the second stage. Here I ceased for the day, having I think ascertained that ferns are endorhizal, and that the primary divisions of the roots hence have sheaths, which adhere to the apex of the root itself.—What a strange union of roots, that of monocotyledons in the main divisions, and of pure acrogens in the minor!!
I cannot help thinking that the secret is hidden in these ramenta, which, as is known, are so universal as obviously to have higher functions than those of mere covering scales. The appearance of those I have described as existing about the points of growth, are exactly the same as the processes mixed with the anthers of mosses, and of which the anthers are nothing but more developed growths; this would point out, as indeed appears to me otherwise evident, (especially from consideration of the theca, and its want of style,) that ferns are lower organised as sexual beings than mosses and Hepaticæ. I know nothing of Lycopodineæ, more than they are the highest of all acrogens; and are not to be included in the same category with ferns.
The objection to the ramenta being anthers, will be the closed nature (apparently) of the terminal cell, and although the anthers of mosses do burst, and most especially those of Hepaticæ, yet the argument is not conclusive—inasmuch as boyaux, to which they are analogous do not open?
These ramenta explain fully the nature of those confervoid organs found in some Neckeræ, and perhaps in other mosses, and it becomes paramount to prove whether these Neckeræ have also the usual anthers, or if they are confined to these, in which case a presumptive proof will thus be afforded of their functions: if they have both forms, they will nevertheless constitute an analogous passage between the two orders: if they have only these, such Neckeræ will form, as indeed they do, a very distinct genus.
The nature of the barren fronds requires distinct analysis. Are they barren from mere deficiency in supplies, such as may result from many circumstances; or are the antheriform ramenta deficient? They are barren from defective growth. I am aware how readily objection may be taken to these views, some will say these young ramenta are nothing but young scales as the older ones evidently are scales; but this amounts to nothing, because we may expect simplicity in the sexual organs of this division, and it will be only a proof of the uniformity of nature in making so great a difference in a function depend on, or be associated with so small a one in form. My view I think explains their uniformly brown colour—analogous to Brown’s sphacelation in mutatis mutandis.
Others will say how absurd the idea is, when you cannot show the place to which the impregnating influence is to be applied. But the consideration of mosses does away with this objection partly, and that of Anthoceros, entirely; because in mosses, the ovule, or pre-existing cell, ready to receive the male influence becomes an empty cell, terminating the seta; and the sporula become developed at its opposite end, the first growth appearing to be quite unconnected with that of the future reproductive organs: and in Anthoceros there is no fixed punctum ready for the application of the male organs, but these have to form a communication with the lower, or inferior cellular tissue of the frond, before even the growth of seta can commence.
Besides a case in point exists in Viscum, or Loranthus, in which no point is ready prepared for the reception of the male influence; showing how universal the law is, that in no one point or place is there an absolute want of gradation.
As in mosses the influence of the male disregarding the ovule, is thrown into the development of the seta, and then of the theca at the apex of this; there can be no conclusive reason why in ferns the same influence should be thrown into the development of the frond, and then into that of the theca.
While Anthoceros proves that in these orders the male influence may exert its effects upon any point.
As there is no styliform production in Anthoceros, so there is none in ferns. If the ramenta be anthers, they will not be dubious ones, because as they remain fixed, people cannot say, that possibly they are also reproductive bodies, which by the bye is no objection at all, after instances of anthers bearing ovules instead of pollen!
Why the peculiar distribution of the male influence (on which we determine our genera,) takes place, is another question, and one that cannot be fairly asked?
Why it is confined to the under surface perhaps can, it being a law that in all cases it is the under surface of the leaf, or its modification, from which new growths originate, and as nature has closed indusia, how could the under surface be interior if this rule were not regularly adhered to?
That the indusium is a special organ, i.e. not an eruption of the cuticle, I am sure; hence it is essential to examine extensively both indusiate and other forms, the precise extension of their veins, etc. at an early period to ascertain if their most diversified situations cannot be reduced to some one type.
Query. Is the gyrate vernation of any ferns comparable to the form of certain shells, to which (at least Mollusca) ferns are supposed to be analogous.
Memo. To ascertain the most peculiar, and most universal points of Mollusca and Pseudo cotyledonea, it is in this way that we may hope to extend our views. Some there are indeed who, while the whole course of their studies has been to neglect structure, deny the applicability of presumptive evidence in favour of doctrines, the subjects of which are barely susceptible of direct proof. Thus Greville and Arnott, angrily ask, what do persons mean by saying that mosses have pistilla, etc.? they protest against such community of application in the use of terms. Many more deny sexuality because it has not been proved. Considering the invisible nature of the fluid of the anthers of mosses, etc. how do they expect that we are to demonstrate its application to the pistil, and the subsequent steps? As well might they doubt the necessity of the application of the boyau to an ovule, (or the existence of the boyau itself,) because the derivation of the embryo cannot be proved.
One word more; in all cases the appearance of the reproductive body after impregnation, is of late date; that date becomes later as we descend the scale. The embryonary sac of Phænogams does not always exist at the time of application of the boyau, and the appearance of the embryo is always posterior to this.
Again, ferns are superior to mosses in this, that in many cases the male influence is exerted directly on the parts that become the thecæ, which is not the case in mosses.
18th.—Continued examining ferns, and to-day completes my knowledge of the ramenta of three different genera.
In the first which is Cryptogamma, the resemblance of the young ramenta to the anthers of Jungermannia is evident enough, they are capital, and the head is at one period filled with granular matter: so are the cells throughout, to a greater or less extent. They are to be seen in all stages of development on the pinnæ of a very young frond, those near its base having perhaps effected their purpose, while those at the apex of the pinna, or the prolonging part of pinnula, may be formed of only one cell. It is curious that the terminal cell does not become spherical for some time: in its earlier stages it is cylindrical like the rest.
The appearances of the old ones are, if possible, more markedly in favour of my hypothesis; there is the same aggregation of grumous congealed matter about the ends of each cell, the same curious communication between these masses which hide the septa from view, evincing a greater or less tendency to assume the peculiar fuscesent or fusco-brown appearance. I observed in two instances what appeared to me decided irregular openings in the terminal cell, from one of which grumous filaments projected; these appeared to communicate with the mass in the terminal cell, which like that in all the others, is congealed; but it assumes a different and very undefined form.
People may object and say, why were not more met with opened? This is no objection, because it is obvious that a spherical body may be opened in part of its surface, and yet unless this portion happens to be on the edge as it were of the sphere, it may escape detection with a microscope of poor penetration.
In this the ramenta are confined, or nearly so, to the under surface of the fronds. Most occupy that which is called the costa. In this the first change as in Adiantum is in the definition of the margin. But this point I have not paid much attention to, as with my present means here, it would be absurd to attempt proving how the fecundation takes place; all that I can attempt is, to ascertain from structure and analogy, the male nature of these curious bodies.
See Plate B for the various sketches. [{450}]
The next genus examined, is perhaps the instance in which these ramenta have the strongest resemblance to ordinary simple hairs, both in their young, when they represent succulent, tinged, grumous molecular-containing hairs, and in the old, when they represent long, flattened, coriaceous hairs, still there is abundant evidence to prove that, however different these bodies are in appearance from those of Cryptogamma, that they undergo the same changes, excepting perhaps as to dehiscence. We have a tendency to fuscous colouring, a tendency to the aggregation of congealed matter about the septæ, precisely the places where it is to be expected. The same appearance of a canal of communication, the same irregular constriction of certain cells; in this too the first change in the pinnæ, or its component lobes, is the definition of the margin. In this genus the under surface of the frond is covered with these hairy-form bodies (which have been figured over and over again in Hooker and Greville’s ferns): on the upper face, a few exist, but incomparably less developed.
From the examination of this genus alone, I do not think the idea I have been so diffuse upon, would have struck me.
To-morrow I examine Ceterach, assured that the scales of its under face are reducible to the same type. In a matter of such interest and importance as this, many will, and with reason, dislike so important an assumption on such inconclusive evidence. But with our present means, it appears to me probable that no evidence to demonstration can be looked for, and for this reason, that the contents of these peculiar cells are so subtile as to escape definition even while in their cells, (or under the most favourable circumstance for a concentration of attention.) How much more so will this be the case, when we attempt to examine the steps of the application of the fecundatory matter, applied over a surface without any prominent points, and probably opaque.
When direct evidence is not to be had, we are justified in using presumptive evidence. As in human law, so in the laws of nature, presumptive evidence to a practised eye carries with it conviction. We have no direct evidence how the embryo is formed, yet no one doubts but that it is brought about by the agency of the boyau, which is a cell containing grumous molecular matter. However different a boyau may seem to many, yet when viewed in conjunction with Cycadeæ, the graduation to the present case becomes natural, and even the resemblance may be perfect, because in Cycas the grains of pollen get into the nucleus bodily, although they would still seem to throw out short tails.
Wonderful is the simplicity of nature! The male organ in its essence, consists of a single cell containing molecular matter.
The female in its essence consists of a single cell, likewise containing similar matter. The influence of the male is exerted, and so another cell is formed in the female cell, and this either becomes the embryo, or gives origin to another cell, and so on, until the terminal one becomes the embryo.
I believe from examination of the most developed scaly ramenta, that these have at an earlier period been fecundating organs, the same peculiarities are to be detected towards their ends, where in fact they retain their original structure, the dilated base being a subsequent development.
In reference to this, the examination of young ferns on their arrival at the age of puberty is indispensable. A curious question arises, what is the frond of a fern? Is it a mass of foliaceous growth containing certain lines of reproductive matter, or is it a distinct development from the axis, in which the reproductive organs are situated? Is it, or is it not, subservient to reproduction? Here again extensive examination is necessary.
If it is altogether subordinate to reproduction, we may expect the occurrence of far more simply constituted ferns than we are yet acquainted with. In fact we may expect a form reduced to an axis, a few ramenta, a frondose dilatation, and one punctum of reproductive organs.
With respect to duration, each frond is analogous to a single seta of a moss, it has definite limits, and is unlike the fronds of certain Hepaticæ, which are capable of compound growth; or if this is the case in ferns, as it is in viviparous ferns, the new formation becomes separated from the frond, as a Phænogamous gemma does. This is a question of importance, as perhaps it may prove that all the foliaceous forms, except Lycopodium, Equisetum, and Chara, are frondose; the dorsal situation is in favour of this assumption, since in all the genuine frondose forms, the reproductive organs of both kinds originate immediately from the under surface, although they may protrude through the upper.
I here ask, is there not primâ facie evidence that these organs have peculiar functions; a peculiar form, attended with peculiar changes, must have peculiar functions; and will any one show me in any single instance, like circumstances to the like extent, in any of those organs called hairs? By the bye, ferns themselves may prove that however like these are to certain forms of hair, yet that their functions are different, because the glandular hairs of ferns do not undergo the same alterations, and are evidently nothing but hairs, probably secretory.
19th.—In Ceterach the same thing occurs precisely, with this difference, that the capita of the ramenta are highly developed; and still more, that the terminations of each pinnula of the young frond, are mere scales without a terminal head.
So that almost all the scales of the under surface of the lobes of the mature frond, are mere scales. The peculiar ramenta are to be looked for along the insertion of each pinna, and along the rachis, in which all have the peculiar structure.
At the time that these scales are commencing their development, the peculiar ones are at the age of mature perfection, so far as function goes. No one can look at a young pinnula at this epoch and observe the evident capitation of each ramentum, the inflexion of its apex, so that the head is brought into contact with the frond, without suspecting that they have the same relation of cause to the appearance subsequently of the thecæ or capsules. It is curious that the colour of the scales is the same as that of the ramenta, in which the colour is developed from above downwards, a peculiarity as it appears to me.
The frond of Ceterach is very frondose-looking, it has stomata on its under surface, and the cells of the cuticle very sinuate. There can be no doubt of the propriety of including the nature of these ramenta and scales in its generic character.
I can see nothing peculiar in the situation of the scales or ramenta to suggest the reason of the situation of the capsules.
In several cases, each pinna appears to have scales only which become barren lobes? the scales and ramenta have the same imbricate situation. In this country it will be useless to expect more proofs. But the four genera alluded to afford evidence enough, and sufficient to show that these ramenta are formed with reference to some important function, that their universality is incompatible with any functions of such minor degree as are attributed to them by those who represent them to be scales or hairs.
To those who require proof of the existence of the complex male organ of Phænogams, or of a male of that form with which only they are familiar, I do not address myself; but to the philosophic botanist, who expects to meet with in the lower orders of plants, a lower organization, one with a tendency of reduction to the essential elements, and who bears in mind the comparative anatomy and structure of similar bodies in adjoining, or not very distant groups, I beg leave to suggest the intimate study of the ramenta of Ferns.
Various as the situation of the fructification is, in three out of the above four genera, yet the initial arrangements are precisely the same. The various forms therefore may not depend proximately on fructification itself, but on the peculiar growth given to the species, in the same way in fact as we have the numerous modifications of the theca in mosses, etc. and the infinite modifications of the carpels in Phænogams.
(Attention is particularly pointed to those ferns which have general capsules or involucres.
Above all to the Cyatheoid forms.
To Ophioglossum.
To naked Thecæ.
To indusiate as Asplenia, etc.)
But however erroneous these views may be, they will still have been of service if general attention is directed by them to plants, in consequence of the suggestions they make. The time now thrown away on isolated species, the station of which, still does not become fixed, when devoted to the philosophical examination of ferns, will rescue botany from one of its numerous reproaches. It is strange that such should exist to the greatest degree in all those families stamped by nature as most distinct. Those chaoses Polypodium, Aspidium, Davallia, would then undergo distinct creation, and the primary divisions of the family would become fixed; and we should then be spared the reproach of drawing characters from organs, of the nature and functions of which we are quite ignorant of, and of the importance of which in a science of demonstration like that of botany, it is impossible to judge, without a true knowledge of structure.
Vide Lindley’s Introd. ed. 2, 407, for the protest of Greville and Arnott.
What is the most comprehensive definition of a pistil. A case in which the future organs of reproduction are developed; and here is a most curious circumstance, namely, that though the calyptra, which is a genuine pistillum containing an ovulum, becomes torn up from its base, yet it remains in contact with that part of the seta in which the sporules are developed until these make their appearance, or even later!! so that one might as well deny a pistillum to a Reseda, or Leontice, as deny it to these plants on the strength of its being torn from its attachments. Sprengel’s objections are worthy only of being noticed from their having been quoted by Lindley. The vagueness of his statement destroys all weight.
His objections in all cases amount to the fact, that the stellulæ or buds containing the anthers are capable of growth. So is the prolongation of an axis of Ananassa.
A Gemma has a general character in its formation as well as an anther, or as pollen; one is a congeries of cellular tissue, with or without vessels, the other a sac consisting of a single cell containing active molecular matter. As an anther producing a single grain of pollen is not inconsistent with our notions of structure, so neither is an anther consisting of a single grain of pollen.
Will any one show me an instance of a proved gemma taking upon itself the form of one of these anthers? Will any show an instance of a sac containing fluid matter capable of growth after dehiscence. The real gemmæ of the Hepaticæ puts the question of gemmæ out of doubt. Is there any plant existing with two sorts of gemmæ, so differently constituted? Many phænogams have gemma in addition to sexes, so have Hepaticæ. Which is the most probable? That they should have no sexes, reproductive organs, and two sorts of gemmæ, or sexes, reproductive organs, or gemmæ of one evident kind?
I cannot adopt the belief of any one having seen the germination of the powder in the axillary bodies, that is, if applicable to the organs I take for anthers.
(Memorandum.—To draw up a parallel between the two sets of organs, and the steps followed in the development of each.)