380 THE SEED AND ITS GERMINATION 



consisting of two valves which grip the cotyledons 

 rather like the two shells of an oyster) and acts as a 

 fulcrum on which the elongating hypocotyl works in 

 pulling the cotyledons out of the testa. 



In the second type of germination the cotyledons 

 remain within the seed (hypogeal 1 ). The hypocotyl 

 does not elongate, but the epicotyledonary bud at 

 once grows out, at the expense of the food stored in 

 the cotyledons, when these are large and swollen as 

 in non-endospermic seeds (Fig. 63, B), (bean, acorn) ; 

 while in endospermic seeds the cotyledon acts as a 

 " sucker," remaining embedded in the endosperm, 

 absorbing and transmitting the soluble foodstuff from 

 the endosperm to the growing parts of the seedling 

 (Fig. 63, C). This is well seen in the monocotyledonous 

 date seed in which the peg-like cotyledon embedded in 

 the endosperm produces cytase, which attacks the solid 

 cellulose of the endosperm and absorbs the sugar pro- 

 duced. In the cereals a special organ, the scutellum, 

 lies between the axis of the embryo and the endosperm, 

 and its surface cells secrete diastase which passes into 

 the starchy endospernr, attacks and hydrolyses the 

 starch grains, the sugar produced being absorbed by 

 the scutellum. In all cases the endosperm or cotyledon 

 cells contain protein grains, the nitrogenous material 

 represented by which is of vital importance in the forma- 

 tion of new protoplasm, though much less in amount 

 than the carbohydrate material. Much of the sugar 

 derived from this latter is broken up in the intense 

 respiration which occurs in the germinating seed. 



The plant may in fact be regarded as living at its 

 highest intensity during germination. At no other time 

 is there so extensive and rapid a mobilisation of food 

 1 VTTO and yfj, below the earth. 



