ALLIUM CEPA 



183 



endosperm in which the coiled embryo lies embedded. (Fig. 83, 

 /4.) The endosperm cells are thick-walled, with a limited number 

 of interconnecting pits. Sachs has shown that the thickening on 

 the walls of the endosperm decreases during germination; and 

 Cooley (3) has confirmed this, pointing out that the reserve hemi- 

 cellulose, laid down on the wall as a secondary product, yields 

 mannose on hydrolysis. The endosperm cells, which retain their 

 protoplasmic contents, contain oil globules and protein, the latter 

 being the first food to be withdrawn during germination. These 

 cells, together with the cells of the haustorial portion of the coty- 



FiG. 83. A, the seed, dotted lines indicate position of the embryo ; B, diagram of embryo ; 

 C, diagram of transection of embryo at level 3-3, in B; D, the same, at level 4-5, showing 

 the slit ; E, the same, showing variation in the slit ; F, the same, at level 6-6 ; G, diagram 

 of longisection of the lower portion of embryo ; H, longisection through haustorial tip of 

 cotyledon showing procambial cells extending to the epidermis which is without a cuticle : 

 cof, cotyledon ; h, hilum ; hyp, hypocotyl ; p, leaf primordium ; p c, procambial strand ; 

 ph, phloem ; s, slit in cotyledon ; st, stem ; v, cavity in hollow base of cotyledon ; x, xylem. 

 (After Hoffman.) 



ledon, function in the absorption and transfer of food; and the 

 endosperm cells do not collapse until all of the reserve cellulose is 

 exhausted. (Fig. 83, /f.) 



The Embryo. — The mature embryo is a curved cylinder about 

 6 mm. long and 0.4 mm. in diameter, the latter being uniform 

 throughout except that the hypocotyl is pointed and the haustorial 

 tip of the cotyledon somewhat rounded. (Fig. 83, B.) The cur- 

 vature of the axis varies from crescentic to more than a complete 

 circle, and, according to Hoffman, a 170° arc is the average. The 

 hypocotyl is small and short, and the major portion of the embryo 

 consists of the cotyledon which arises from the cotyledonary node 



