78 



HYPOCOTYLS, EPICOTYLS, ETC., Chap, rt 



Cyclamen, 

 seedling, 



bioaks tnrough the ground as an arch (Fig. 57). 

 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. 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 

 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 Cycas 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 



isanihus mollis: seedling, with the ^yith the petiole at first UOt 

 hypogean cotyledon on thn near , ,« ,^■^ j.i j. i? xi, 



side removed ind the radicles cut halt aS thick aS that Ot the 



off: a, blade of first leaf begin- ofher. The Undeveloped 



ning to e,\pand, with petiole still , » . , ■, -, 



paitiallj arched; 6, second and leaf IS protected by Stand- 



ovpositejeaf, as yet very im,.er- -j, beneath itS aichcd fel- 



tectly developed ; c, hypogean o 



cotyledon on the opposite side. low ; and it is an instruc* 



Peraicurn : 

 figure en- 

 larged : c, blade of 

 cotyledon, not yet 

 expanded, with arched 

 petiole beginning to 

 straighten itself; /i, 

 hypocotyl developed 

 into a corm ; r, second- 

 ary radicles. 



Fig. 58. 



