Dahlias propagated by tubers under the hot climate of St. Domingo vary much; Sir R. Schomburgk gives the case of the "Butterfly variety," which the second year produced on the same plant "double and single flowers; here white petals edged with maroon; there of a uniform deep maroon." (11/77. 'Journal of Proc. Linn. Soc.' volume 2 Botany page 132.) Mr. Bree also mentions a plant "which bore two different kinds of self-coloured flowers, as well as a third kind which partook of both colours beautifully intermixed." (11/78. Loudon's 'Gardener's Mag.' volume 8 1832 page 94.) Another case is described of a dahlia with purple flowers which bore a white flower streaked with purple. (11/79. 'Gard. Chronicle' 1850 page 536; and 1842 page 729.)
Considering how long and extensively many Bulbous plants have been cultivated, and how numerous are the varieties produced from seed, these plants have not perhaps varied so much by offsets,—that is, by the production of new bulbs,—as might have been expected. With the Hyacinth, however, several instances have been given by M. Carriere. A case also has been recorded of a blue variety which for three successive years gave offsets producing white flowers with a red centre. (11/80. 'Des Jacinthes' etc. Amsterdam 1768 page 122.) Another hyacinth bore (11/81. 'Gardener's Chronicle' 1845 page 212.) on the same truss a perfectly pink and a perfectly blue flower. I have seen a bulb producing at the same time one stalk or truss with fine blue flowers, another with fine red flowers, and a third with blue flowers on one side and red on the other; several of the flowers being also longitudinally striped red and blue.
Mr. John Scott informs me that in 1862 Imatophyllum miniatum, in the Botanic Gardens of Edinburgh, threw up a sucker which differed from the normal form, in the leaves being two-ranked instead of four-ranked. The leaves were also smaller, with the upper surface raised instead of being channelled.
In the propagation of TULIPS, seedlings are raised, called selfs or breeders, which, "consist of one plain colour on a white or yellow bottom. These, being cultivated on a dry and rather poor soil, become broken or variegated and produce new varieties. The time that elapses before they break varies from one to twenty years or more, and sometimes this change never takes place." (11/82. Loudon's 'Encyclopaedia of Gardening' page 1024.) The broken or variegated colours which give value to all tulips are due to bud-variation; for although the Bybloemens and some other kinds have been raised from several distinct breeders, yet all the Baguets are said to have come from a single breeder or seedling. This bud-variation, in accordance with the views of MM. Vilmorin and Verlot (11/83. 'Production des Varietes' 1865 p. 63.) is probably an attempt to revert to that uniform colour which is natural to the species. A tulip, however, which has already become broken, when treated with too strong manure, is liable to flush or lose by a second act of reversion its variegated colours. Some kinds, as Imperatrix Florum, are much more liable than others to flushing; and Mr. Dickson maintains (11/84. 'Gardener's Chronicle' 1841 page 782; 1842 page 55.) that this can no more be accounted for than the variation of any other plant. He believes that English growers, from care in choosing seed from broken flowers instead of from plain flowers, have to a certain extent diminished the tendency in flowers already broken to flushing or secondary reversion. Iris xiphium, according to M. Carriere (page 65), behaves in nearly the same manner, as do so many tulips.
During two consecutive years all the early flowers in a bed of Tigridia conchiflora (11/85. 'Gardener's Chron.' 1849 page 565.) resembled those of the old T. pavonia; but the later flowers assumed their proper colour of fine yellow, spotted with crimson. An apparently authentic account has been published (11/86. 'Transact. Lin. Soc.' volume 2 page 354.) of two forms of Hemerocallis, which have been universally considered as distinct species, changing into each other; for the roots of the large-flowered tawny H. fulva, being divided and planted in a different soil and place, produced the small-flowered H. flava, as well as some intermediate forms. It is doubtful whether such cases as these latter, as well as the "flushing" of broken tulips and the "running" of particoloured carnations,—that is, their more or less complete return to a uniform tint,—ought to be classed under bud-variation, or ought to be retained for the chapter in which I treat of the direct action of the conditions of life on organic beings. These cases, however, have this much in bud-variation, that the change is effected through buds and not through seminal reproduction. But, on the other hand, there is this difference—that in ordinary cases of bud- variation, one bud alone changes, whilst in the foregoing cases all the buds on the same plant were modified together. With the potato, we have seen an intermediate case, for all the eyes in one tuber simultaneously changed their character.
I will conclude with a few allied cases, which may be ranked either under bud-variation, or under the direct action of the conditions of life. When the common Hepatica is transplanted from its native woods, the flowers change colour, even during the first year. (11/87. Godron 'De l'Espece' tome 2 page 84.) It is notorious that the improved varieties of the Heartsease (Viola tricolor), when transplanted, often produce flowers widely different in size, form, and colour: for instance, I transplanted a large uniformly-coloured dark purple variety, whilst in full flower, and it then produced much smaller, more elongated flowers, with the lower petals yellow; these were succeeded by flowers marked with large purple spots, and ultimately, towards the end of the same summer, by the original large dark purple flowers. The slight changes which some fruit-trees undergo from being grafted and regrafted on various stocks (11/88. M. Carriere has lately described in the 'Revue Horticole' December 1, 1866 page 457, an extraordinary case. He twice inserted grafts of the Aria vestita on thorn- trees (epines) growing in pots; and the grafts, as they grew, produced shoots with bark, buds, leaves, petioles, petals, and flower-stalks, all widely different from those of the Aria. The grafted shoots were also much hardier, and flowered earlier, than those on the ungrafted Aria.) were considered by Andrew Knight (11/89. 'Transact. Hort. Soc.' volume 2 page 160.) as closely allied to "sporting branches," or bud-variations. Again, we have the case of young fruit-trees changing their character as they grow old; seedling pears, for instance, lose with age their spines and improve in the flavour of their fruit. Weeping birch-trees, when grafted on the common variety, do not acquire a perfect pendulous habit until they grow old: on the other hand, I shall hereafter give the case of some weeping ashes which slowly and gradually assumed an upright habit of growth. All such changes, dependent on age, may be compared with the changes, alluded to in the last chapter, which many trees naturally undergo; as in the case of the Deodar and Cedar of Lebanon, which are unlike in youth, whilst they closely resemble each other in old age; and as with certain oaks, and with some varieties of the lime and hawthorn. (11/90. For the cases of oaks see Alph. De Candolle in 'Bibl. Univers.' Geneva November 1862; for limes etc. Loudon's 'Gard. Mag.' volume 11 1835 page 503.)]
GRAFT-HYBRIDS.
Before giving a summary on Bud-variation I will discuss some singular and anomalous cases, which are more or less closely related to this same subject. I will begin with the famous case of Adam's laburnum or Cytisus adami, a form or hybrid intermediate between two very distinct species, namely, C. laburnum and purpureus, the common and purple laburnum; but as this tree has often been described, I will be as brief as I can.
[Throughout Europe, in different soils and under different climates, branches on this tree have repeatedly and suddenly reverted to the two parent species in their flowers and leaves. To behold mingled on the same tree tufts of dingy-red, bright yellow, and purple flowers, borne on branches having widely different leaves and manner of growth, is a surprising sight. The same raceme sometimes bears two kinds of flowers; and I have seen a single flower exactly divided into halves, one side being bright yellow and the other purple; so that one half of the standard-petal was yellow and of larger size, and the other half purple and smaller. In another flower the whole corolla was bright yellow, but exactly half the calyx was purple. In another, one of the dingy-red wing-petals had a narrow bright yellow stripe on it; and lastly, in another flower, one of the stamens, which had become slightly foliaceous, was half yellow and half purple; so that the tendency to segregation of character or reversion affects even single parts and organs. (11/91. For analogous facts see Braun 'Rejuvenescence' in 'Ray Soc. Bot. Mem.' 1853 page 320; and 'Gardener's Chronicle' 1842 page 397; also Braun in 'Sitzungsberichte der Ges. naturforschender Freunde' June 1873 page 63.) The most remarkable fact about this tree is that in its intermediate state, even when growing near both parent-species, it is quite sterile; but when the flowers become pure yellow or pure purple they yield seed. I believe that the pods from the yellow flowers yield a full complement of seed; they certainly yield a larger number. Two seedlings raised by Mr. Herbert from such seed (11/92. 'Journal of Hort. Soc.' volume 2 1847 page 100.) exhibited a purple tinge on the stalks of their flowers; but several seedlings raised by myself resembled in every character the common laburnum, with the exception that some of them had remarkably long racemes: these seedlings were perfectly fertile. That such purity of character and fertility should be suddenly reacquired from so hybridised and sterile a form is an astonishing phenomenon. The branches with purple flowers appear at first sight exactly to resemble those of C. purpureus; but on careful comparison I found that they differed from the pure species in the shoots being thicker, the leaves a little broader, and the flowers slightly shorter, with the corolla and calyx less brightly purple: the basal part of the standard-petal also plainly showed a trace of the yellow stain. So that the flowers, at least in this instance, had not perfectly recovered their true character; and in accordance with this, they were not perfectly fertile, for many of the pods contained no seed, some produced one, and very few contained as many as two seeds; whilst numerous pods on a tree of the pure C. purpureus in my garden contained three, four, and five fine seeds. The pollen, moreover, was very imperfect, a multitude of grains being small and shrivelled; and this is a singular fact; for, as we shall immediately see, the pollen-grains in the dingy-red and sterile flowers on the parent-tree, were, in external appearance, in a much better state, and included very few shrivelled grains. Although the pollen of the reverted purple flowers was in so poor a condition, the ovules were well formed, and the seeds, when mature, germinated freely with me. Mr. Herbert raised plants from seeds of the reverted purple flowers, and they differed a VERY LITTLE from the usual state of C. purpureus. Some which I raised in the same manner did not differ at all, either in the character of their flowers or of the whole bush, from the pure C. purpureus. Prof. Caspary has examined the ovules of the dingy-red and sterile flowers in several plants of C. adami on the Continent (11/93. See 'Transact. of Hort. Congress of Amsterdam' 1865; but I owe most of the following information to Prof. Caspary's letters.) and finds them generally monstrous. In three plants examined by me in England, the ovules were likewise monstrous, the nucleus varying much in shape, and projecting irregularly beyond the proper coats. The pollen grains, on the other hand, judging from their external appearance, were remarkably good, and readily protruded their tubes. By repeatedly counting, under the microscope, the proportional number of bad grains, Prof. Caspary ascertained that only 2.5 per cent were bad, which is a less proportion than in the pollen of three pure species of Cytisus in their cultivated state, viz., C. purpureus, laburnum, and alpinus. Although the pollen of C. adami is thus in appearance good, it does not follow, according to M. Naudin's observation (11/94. 'Nouvelles Archives du Museum' tome 1 page 143.) on Mirabilis, that it would be functionally effective. The fact of the ovules of C. adami being monstrous, and the pollen apparently sound, is all the more remarkable, because it is opposed to what usually occurs not only with most hybrids (11/95. See on this head Naudin ibid page 141.), but with two hybrids in the same genus, namely in C. purpureo-elongatus, and C. alpino-laburnum. In both these hybrids, the ovules, as observed by Prof. Caspary and myself, were well-formed, whilst many of the pollen-grains were ill-formed; in the latter hybrid 20.3 per cent, and in the former no less than 84.8 per cent of the grains were ascertained by Prof. Caspary to be bad. This unusual condition of the male and female reproductive elements in C. adami has been used by Prof. Caspary as an argument against this plant being considered as an ordinary hybrid produced from seed; but we should remember that with hybrids the ovules have not been examined nearly so frequently as the pollen, and they may be much oftener imperfect than is generally supposed. Dr. E. Bornet, of Antibes, informs me (through Mr. J. Traherne Moggridge) that with hybrid Cisti the ovarium is frequently deformed, the ovules being in some cases quite absent, and in other cases incapable of fertilisation.
Several theories have been propounded to account for the origin of C. adami, and for the transformations which it undergoes. The whole case has been attributed by some authors to bud-variation; but considering the wide difference between C. laburnum and purpureus, both of which are natural species, and considering the sterility of the intermediate form, this view may be summarily rejected. We shall presently see that, with hybrid plants, two embryos differing in their characters may be developed within the same seed and cohere; and it has been supposed that C. adami thus originated. Many botanists maintain that C. adami is a hybrid produced in the common way by seed, and that it has reverted by buds to its two parent-forms. Negative results are not of much value; but Reisseck, Caspary, and myself, tried in vain to cross C. laburnum and purpureus; when I fertilised the former with pollen of the latter, I had the nearest approach to success, for pods were formed, but in sixteen days after the withering of the flowers, they fell off. Nevertheless, the belief that C. adami is a spontaneously produced hybrid between these two species is supported by the fact that such hybrids have arisen in this genus. In a bed of seedlings from C. elongatus, which grew near to C. purpureus, and was probably fertilised by it through the agency of insects (for these, as I know by experiment, play an important part in the fertilisation of the laburnum), the sterile hybrid C. purpureo-elongatus appeared. (11/96. Braun in 'Bot. Mem. Ray. Soc.' 1853 page 23.) Thus, also, Waterer's laburnum, the C. alpino-laburnum (11/97. This hybrid has never been described. It is exactly intermediate in foliage, time of flowering, dark striae at the base of the standard petal, hairiness of the ovarium, and in almost every other character, between C. laburnum and alpinus; but it approaches the former species more nearly in colour, and exceeds it in the length of the racemes. We have before seen that 20.3 per cent of its pollen-grains are ill-formed and worthless. My plant, though growing not above thirty or forty yards from both parent-species, during some seasons yielded no good seeds; but in 1866 it was unusually fertile, and its long racemes produced from one to occasionally even four pods. Many of the pods contained no good seeds, but generally they contained a single apparently good seed, sometimes two, and in one case three seeds. Some of these seeds germinated, and I raised two trees from them; one resembles the present form; the other has a remarkable dwarf character with small leaves, but has not yet flowered.) spontaneously appeared, as I am informed by Mr. Waterer, in a bed of seedlings.