94 



SEED. 



tion of the chalaza is distinctly marked by a small dark-colored 

 spot. The raphe does not always consist of a single bundle of 

 vessels, but ramifies on the surface of the seed, as may be seen 

 by the veins on the surface of the Almond, which are ramifica- 

 tions of the raphe. 



163. The embryo is the product of the action of the pollen. 

 If the ovule be dissected soon after impregnation, there will be 

 found within the nucleus and contiguous to the foramen a 

 minute speck, opake and yellowish, which enlarges by the ab- 

 sorption of the surrounding fluid : this fluid is the amnios. The 

 minute speck becomes in its enlargement a distinctly organized 

 body, and assumes in time the form of an embryo plant. The 

 embryo consists of three parts, the radicle, plumula, and cotyle- 

 don ; some add a fourth, a cauliculus or neck. The radicle be- 

 comes by development the root or descending axis of the plant, 

 and the plumula the ascending axis or stem. The cotyledons 

 are to be the earliest leaves of the plant. The cauliculus or neck 

 is the imaginary point of separation of the plumula from the 

 radicle. Fig. 161 represents a young dicotyledonous plant — 

 a the plumula, r the radicle, c c the cotyledons, t the cauliculus 

 or neck. 



Fig. 161. 



Fig. 162. 



* 



Young Dicotyledon. 

 a, plumula ; cc, cotyledons ; t, cauliculus , 

 r, radicle. 



Young Monocotyledon. 



co, cotyledon ; col, coleorhiza ; 



rad, radicle. 



164. The radicle of the monocotyledon is inclosed within a 

 sheath which it perforates in its elongation, and issues from be- 

 tween its lips, as seen in Fig. 162 — rad being the radicle, col 

 the coleorhiza, co the cotyledon. This sheath Mirbel called a 

 coleorhiza, and Richard proposed to substitute Endorhizm for 

 monocotyledons, and JExorhizce for dicotyledons, thus founding 



163. What is the embryo 1 Of how many parts does it consist? What 

 do these parte become ' — L84. Ilow is the radicle in monocotyledons? 

 What did Kichard call monocotyledons ? What dicotyledons ? 



