136 A TEXT-BOOK OF GRASSES 



GERMINATION 



170. The situation of the embryo in the grass seed is 

 such that by the enlargement and growth of the organs 

 the plumule and root at once emerge in opposite direc- 

 tions. The seed remains in position, which is usually 

 upon the surface of the ground. The primary root at 

 first elongates but soon secondary roots appear which in 

 a short time exceed the primary. The plumule pushes up 

 somewhat later. The first leaf of the plumule acts as a 

 protecting sheath and never develops into a foliage leaf. 

 If the seed is below the surface of the soil this sheath, 

 closed at the apex, elongates until the surface is reached, 

 when the tip breaks and the bud pushes through. In 

 many embryos there is a small scale-like organ (epiblast) 

 at the base of the plumule opposite the scutellum. This 

 is thought by some to represent a leaf, in which case the 

 scutellum is the first leaf or cotyledon, and the pro- 

 tecting sheath of the plumule is the third leaf. 



171. The germination of the maize is described at 

 length by Collins. The protecting sheath he calls the 

 coleoptyle. Between the coleoptyle and the seed is a more 

 or less elongated axis to which the name mesocotyl is 

 given. This portion is called by Hackel and others the 

 epicotyl on the supposition that it is an internode above 

 the cotyledon or scutellum. Collins and others consider 

 the scutellum, epiblast and coleoptyle to be all parts of a 

 highly specialized cotyledon. Collins also describes the 

 germination of Hopi and Navajo varieties of maize in 

 which the mesocotyl elongates greatly, reaching the 

 enormous length of 25 or even 30 cm. The plumule is 

 thus able to reach the surface from a corresponding depth. 

 Such varieties are adapted to dry regions. The usual 



