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Show 9Q RUDIMENTARY CO'l'YI .. EDONS. CIIAl'. II. specimen was only Tboth and in ano.ther cfo-th inch in leno-th · it ultimately appeared as 1f seated halfway Jo,;n tj1o hypocotyl. In both these species the hypocotyl is so much enlarged, especially at a very early age, that it might almost .be ~alled a corm. Th? low~r end forms a heel or proJeCtiOn, tho use of whiCh w1ll hereafter be described. In Cyclamen Persic1~m the hypocotyl, even whilst still within tho seed, is enlarged into a regular corm,* and only a single cotyledon is at first ~eveloped (sec former Fig. 57.) With Ranunculus ficana two cotyledon~ are never produced, and here one of the seconLlary rachcles is developed at an early age into a so-called bulb:t Again, certain species of Ch::erophyll:1m and Corydalis produce only a single cot}leclon; + 1~ th~ former the hypocotyl, and in the latter tho radwle IS enlarged, according to Irmisch, into a bulb. In the several foregoing cases one of the cotyledons is delayed in its development, or reduced in. si~c, or rendered rudimentary, or quite aborted ; but m oth~r cases both cotyledons are represented by mere nu!Jmonts. With Opuntia basilar1's this is not . the case, for both cotyledons are thick and large, and the hypocotyl shows at first no signs of enlargement; b.ut afterwards, when the cotyledons have withered and disarticulated themselves, it becomes thickened, and from jts tapering form, together with its smooth, tough, brown skin, appears, when ultimately drawn down to some depth into the soil, like a root. On tho other * Dr. H. Gressner, 'Bot. Zeitullg.' 1874, p. 824. t Irmisch, • Deitl'age zur Morphologie der Pflanzen,' 1854, pp. l 1, 1~; 'Bot. Zeitung,' 1874, p. 805. t Delpino, 'Rivisfo. Bofanico.,' l877, p. 2J. It ia cvidcut from Vauclier's account (' H ist. PhyH. des Plantes d'Europe,' tom i.1841, p. 149) of tho frCrmiD:ntion of tho seeds of sevoml · species of Cory· dalis that 1ho bulb or tubercula bo~i1~s to be form ed n.t an ex· treruoly early age. CHAP. II. RUDIMEN'fARY CO'fYLEDONS. 97 hand, with several other Oacte::e, the hypocotyl is from the :first much enlarged, and both cotyledons arc almost or quite ruLlimentary. Thus with Cereus Landbeckii two little triangular projections, representing the cotyledons, are narrower than the hypocotyl, which is pear-shaped, with the point downwards. In Rhipsalis cassytha the cotyledons are represented by mere points on the enlarged hypocotyl. In Echinocactus viridescens the hypocotyl is globular, with two little prominences on its summit. In Pilocereus Houlletii tho hypocotyl, much swollen in the upper part, is merely notched on the summit; and each side of the notch evidently represents a cotyledon. Stapelia sarpedon, a member of the very distinct family of the .Asclepiadere, is fleshy like a cactus ; and here again the upper part of the fiattened hypocotyl is much thickened and bears two minute coty~ ledons, which, measured internally, were only ·15 inch in length, and in breadth not equal to one-fourth of the diameter of the hypoeotyl in its narrow axis; yet these minute cotyledons are probably not quite useless, for when the hypocotyl breaks through the ground in the form of an arch, they are closed or pressed against one another, and thus protect the plumule. They afterwards open. From the several oases now given, which refer to widely distinct plants, we may infer that there is some close connection between the reduced size of one or both cotyledons and the formation, by the enlargement of the hypocotyl or of the radicle, of a so-called bulb. But it may be asked, did tho cotyledons first tend to abort, or did a bulb first ucgin to be formed? As all dicotyledons naturally produce two well-developed cotyledons, whilst the thickness of the hypocotyl and of the radicle differs much in different plants, it seems probable that these latter organs first became from H .: !:;; ,t :·')•·, IW'" 1':·:':: 1 ') " |