Fig. 61. Abronia umbellata: seedling twice natural size: c cotyledon; c’, rudimentary cotyledon; h, enlarged hypocotyl, with a heel or projection (h’) at the lower end; r, radicle. [14] In Pachira aquatica, as described by Mr. R. I. Lynch (‘Journal Linn. Soc. Bot.’ vol. xvii. 1878, p. 147), one of the hypogean cotyledons is of immense size; the other is small and soon falls off; the pair do not always stand opposite. In another and very different water-plant, ‘Trapa natans’, one of the cotyledons, filled with farinaceous matter, is much larger than the other, which is scarcely visible, as is stated by Aug. de Candolle, ‘Physiologie Veg.’ tom. ii. p. 834, 1832. With Abronia umbellata one of the cotyledons is quite rudimentary, as may be seen (c’) in Fig. 61. In this specimen it consisted of a little green flap, 1/84th inch in length, destitute of a petiole and covered with glands like those on the fully developed cotyledon (c). At first it stood opposite to the larger cotyledon; but as the petiole of the latter increased in length and grew in the same line with the hypocotyl (h), the rudiment appeared in older seedlings as if seated some way down the hypocotyl. With Abronia arenaria there is a similar rudiment, which in one specimen was only 1/100th and in another 1/60th inch in length; it ultimately appeared as if seated halfway down the hypocotyl. In both these species the hypocotyl is so much enlarged, especially at a very early age, that it might almost be called a corm. The lower end forms a heel or projection, the use of which will hereafter be described. In _Cyclamen Persicum_ the hypocotyl, even whilst still within the seed, is enlarged into a regular corm,[15] and only a single cotyledon is at first developed (see former Fig. 57). With _Ranunculus ficaria_ two cotyledons are never produced, and here one of the secondary radicles is developed at an early age into a so-called bulb.[16] Again, certain species of Chaerophyllum and Corydalis produce only a single cotyledon;[17] in the former the hypocotyl, and in the latter the radicle is enlarged, according to Irmisch, into a bulb. [15] Dr. H. Gressner, ‘Bot. Zeitung,’ 1874, p. 824. [16] Irmisch, ‘Beiträge zur Morphologie der Pflanzen,’ 1854, pp. 11, 12; ‘Bot. Zeitung,’ 1874, p. 805. [17] Delpino, ‘Rivista Botanica,’ 1877, p. 21. It is evident from Vaucher’s account (‘Hist. Phys. des Plantes d’Europe,’ tom. i. 1841, p. 149) of the germination of the seeds of several species of Corydalis, that the bulb or tubercule begins to be formed at an extremely early age.