42 OUTLINE OF STRUCTURAL BOTANY 
The embryo, which lies at the base of the single cotyledon of the 
grain of wheat and almost straight between the lobes of the bean 
may curve around the albumen mass in the seeds of certain plants 
and from the fact of the encircling of the albumen by the embryo 
of such plants, as for example, the Corn Cockle, and many other 
plants of the pink family, this feature is an important element in 
the classification of the plants. In still other seeds the albuminous 
mass completely encloses the embryo. 
It is unnecessary here to discuss the processes attending the 
Fic. 68 Fie. 69 Fic. 70 Fie. 71 
germination of the seed beyond mentioning some of the more obvi- 
ous phenomena. Under the influence of the air, of moisture and 
of a certain degree of heat the parts enclosed within the mem- 
braneous or woody coverings swell and break through the outer wall 
by separating its parts at certain seams or joints, or tearing it in 
an irregular manner. Thus the young plant commences an inde- 
pendent existence. 
The plumule of a seed which has been buried in the soil pushes 
toward the ‘light and air while the radicle. penetrates even deeper 
into the soil. At this stage the cotyledon may, as it usually does 
in case of plants of the dicotyledonous class, cling.one to one side 
of the little stem, the other to the other side and as the stem pushes 
upward they appear above ground as the two first leaves as we see 
them in the fleshy seed leaves of the bean (Fig. 67). As the expan- 
sion of the plumule proceeds the characteristic leaves of the plant 
appear as we see them in the young maple shown at Fig. 68. At 
Fig. 69 we see a young oak, one of the cotyledons of which has not 
yet thrown off the shell of the acorn. 
