24 STUDY OF COMMON PLANTS. 



great classes, howevei-, are as strongly marked as they 



were in the seed, and each class exhibits in its seedlings 



characteristic, though not always distinctive, habits. 



The radicle of dicotyledonous seedlings elongates and 



extends downwards as the primary root, and at the same 



time in most species grows upward, forming the 



nonsseed- " hypocotyl," at the upper extremity of which 



''^^' the cotyledons are borne. In some species, as 



in the pea, the hypocotyl is wanting, or is extremely short, 



the cotyledons remaining in the ground instead of being 



lifted into the air. In such cases a rapid development of 



the "epicotyl," or first internode of the plumule, takes 



place, thus securing to the young leaves as they unfold 



full exposure to air and light. The hypocotyl (or, if this 



is wanting, the epicotyl) breaks through the ground in the 



form of an arch, an arrangement for the protection of the 



delicate growing point.i 



Monocotyledonous seedlings exhibit considerable variety 



among themselves, although several pretty distinct types 



, , may be recognized. In the grasses the scutel- 

 Monoootyledo- r -i 



nous seed- lum, which represents a part of the cotyledon, 



^^^' remains enclosed in the grain, and the straight 



plumule is erect, instead of arched, as it breaks through 

 the ground. In many other species, as for example the 

 date palm, a peculiar modification of this mode of germi- 

 nation is seen. As before, a part of the cotyledon remains 

 in the seed as an organ of absorption, but the other end 

 elongates and grows downward, forming a sheath from 

 which the first leaf afterward emerges .^ A more or less 

 conspicuous primary root may be present, as in Indian 



' Cf. Darwin, Power of Movement in Plants, pp. 87, 88. 

 2 See figures of palm seedling, Goebel, Classification and Special Mor- 

 phology of Plants, p. 432, 



