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.