DICOTYLEDON ES. 



475 



root) ends in a very short root, which is continuous with the stem.* 

 Under the proper conditions of heat and moisture, the root elongates 

 and pushes out through the micro- 

 pyle of the seed-coat ; at the same 

 time, the stalks of the cotyledons 

 elongate and thus bring the plumule 

 outside of the seed-coat, the cotyle- 

 dons alone remaining. During the 

 first few days of its growth the 

 young plant is nourished by the 

 starch in the cotyledons, which in 

 this species remain during the whole 

 process of germination beneath the 

 ground enclosed in the seed-coat. In 

 the common Field Bean (Phascolus) 

 the germination is the same, except- 

 ing that the hypocotyledonary stem 

 elongates, and brings the cotyledons 

 which have slipped out of the seed- 

 coat above the ground. 



The seed of Eicinus (the Castor 

 Oil Plant) contains a large embryo 

 surrounded by a thin layer of endo- 

 sperm (Fig. 368, /). In its germina- 

 tion the root and hypocotyledonary 

 stem elongate, and thus bring the 

 seed-coat with the contained coty- 

 ledons above the ground (Fig. 368, 

 //.). The cotyledons remain within 

 the seed-coat until they have absorb- 

 ed all of the endosperm ; when this 

 is accomplished the empty seed-coat 

 falls away, and the freed cotyledons 

 expand and assume to some extent 

 the function of ordinary foliage 

 leaves. 



The venation of the leaves of Di- 

 cotyledons is easily studied by mac- 

 erating them so as to remove the cotyledons. ss.'apex of" the stem , , 

 * , ,,. , Of tne root ; ct. BWGuttlff near insertion 



parenchyma (mesophyll), leaving of cotyledons i, the Irst Interaode" 

 only the fibro-vascular bundles, fi the Petioles of the first foliage 

 wvii xi " i leaves ; . , /, procambium of the 



While there is as a rule a general flbro- vascular bandies ho hypocoty- 



likeness between them, there is yet SS^I^^r^SlSSS 

 an almost infinite diversity in the Sachs. 



* In some old books, and even a few recent ones, a structure called 

 the collar or collwn is spoken of. Dr. Gray very properly defines it as 



