OP THE EMBRYO AND SEEDLING. 



19 



32. Thus, in the Pea, near relative of the Bean, the embryo 



(Fig. 37), which is the whole kernel of the seed, has the 



cotyledons so gorged with this nutritive 



store that they are hemispherical ; and 



the acorn of the Oak (Fig. 39), near 



relative of the Beech, is in similar case. 



These extremely obese cotyledons have 



not only lost all likeness to leaves, but all 



power of fulfilling the office of foliage, 



which is apparently no disadvantage ; for 



when two different duties are performed 



by the same organ, it rarely performs both 



equally well. Here they become mere 



receptacles of prepared food-, the nature 



and office of which is the same as of the 



albumen, or nutritive deposit exterior to 



the embrj-o in what are called albuminous 



seeds. (25-27.) The difference is in the 



place rather than in the character of the 



deposit. The plumule in such cases is 



always apparent before germination ; and 

 it develops even with more vigor than in 

 the preceding cases. It usually rises as a 

 stout stem of several internodes lengthen- 

 ing almost simultaneously, or at least the 

 upper strongly developing long before the 

 lower have finished their growth ; and 

 the latter are practically leafless, bearing 

 only small and scale-like and useless ru- 

 diments of leaves. This is correlated with 

 the peculiarity that the caulicle does not 

 lengthen in germination, or it lengthens 

 very slightly ; the cotyledons remain within 

 the coats of the seed ; and if this were 

 buried beneath the surface of the ground, there it remains. The 

 abortion of the earliest leaves of the plumule is in correlation 

 with this hypogceous (i. e. underground) situation of the cotyle- 

 dons throughout the germination. The slight elongation of the 

 caulicle serves merely to protrude its root-end from the coats of 

 the seed in a downward direction, and from this a strong root 

 usually is formed. 



FIG. 39. Section of an acorn, filled by the embryo. 40. Advanced germination ot 

 the same. 



