78 



HYPOCOTYLS, EPICOTYLS, ETC., CHAP. IL 



breaks through the ground as an arch (Fig. 57). 



Fig. 57. 



Cyclamen 



Abronia also has only a single fully 

 developed cotyledon, but in this 

 case it is the hypocotyl which first 

 emerges and is arched. Abronia 

 umbellata, however, presents this 

 peculiarity, that the enfolded blade 

 of the one developed cotyledon 

 (with the enclosed endosperm) 

 whilst still beneath the surface has 



straighten itself; A, 



hiTaOTrm ; r,Iecond- 

 ary radicles. 



1?' KQ 



Persicum : 



cfTdeTf its apex upturned and parallel to 

 cotyledon, not yet the descending leg of the arched 

 hypocotyl ; but it is dragged 

 O11 t of the ground by the con- 

 tinned growth of the hypocotyl, 

 w ith the apex pointing downward. 

 With Cyeas pectinata 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 



Acanthus moUis: seedling, with the with the petiole at first not 



^^d^W- 1 ^ half as thick as that of the 



off: a, blade of first leaf begin- o t ne r. The Undeveloped 



S:Tit-" leaf is protected by stand- 



opposite leaf, as yet very imper- - nff beneath its arched fel- 



fectly developed; c, hypogean s . 



cotyledon on the opposite side. low J and it IS an lUStrUC- 



