78 



HYPOCOTYLS, EPICOTYLS, ETC., Chap. It. 



oroalis tnrough 



Fig. 57. 



the ground as an arch (Fig. 57). 

 Abronia also has only a single fully 

 developed cotyledon, but in this 

 case it is the hypocotyl which first 

 emerges and is arched. Ahronia 

 umbellata, howeverj presents this 

 peculiarity, that the enfolded blade 

 of the one deyeloped cotyledon 

 (with the enclosed endosperm) 

 whilst still beneath the surface has 

 its apex upturned and parallel to 

 the descending leg of the arched 

 hypocotyl ; but it is dragged 

 out of the ground by the con- 

 tinued growth of the hypocotyl, 

 with the apex pointing downward. 

 With Gyeas pedinata the cotyledons are hypogean, 



and a true leaf first breaks 

 through the ground with 

 its petiole forming an 

 arch. 



In the genus Acanthus 

 the cotyledons are likewise 

 hypogean. In A. mollis, 

 a single leaf first breaks 

 through the ground with 

 its petiole arched, and with 

 the opposite leaf much less 

 developed, short, straight, 

 of a yellowish colour, and 

 with the petiole at first not 

 half as thick as that of the 

 other. The undeveloped 

 leaf is protected by stand- 

 ing beneath its arched fel- 

 low ; and it is an instruo- 



Cyclamen Persicum : 

 seedling, figure en- 

 larged : <-■, blade of 

 cotyledon, not yet 

 e.\panded, with arched 

 petiole beginning to 

 straighten itself; A, 

 hypocotyl developed 

 intoacorm ; r, second- 

 ary radicles. 



Fig. 58. 



iamthus mollis : seedling, with the 

 hypogean cotyledon on the near 

 side removed and the radicles cut 

 off; •', blade of first leaf begin- 

 ning to expand, with petiole still 

 paitially arched; 6, second and 

 opposite leaf, as yet very imper- 

 fectly developed ; c, hypogean 

 cotyledon on the opposite side. 



