322 



HOW CROPS GROW. 



germinating seed, the change goes on at ordinary or even 

 low temperatures. 



It is generally taught that oxygen acting on the album 

 inoids in presence of water and within a certain range of 

 temperature induces the decomposition which confers on 

 them the power in question. 



The necessity for oxygen in the act of germination has 

 been thus accounted for, as needful to the solution of 

 the starch, etc., of the cotyledons. 



This may be true at first, but, as we shall presently see, 

 the chief action of oxygen is probably of another kind. 



How diastase or other similar substances accomplish the 

 change in question is not certainly known. 



Soluble Starch, The conversion of starch into sugar 

 and dextrin is thus in a sense explained. This is not, how 

 ever, the only change of 

 which starch is susceptible. 

 In the bean, (Phaseolus 

 multiflorus], Sachs (Sitz- 

 unysberichte der &quot;Wiener 

 Akad., XXXVII, 57) in 

 forms us that the starch of 

 the cotyledons is dissolved, 

 passes into the seedling, and 

 reappears (in part, at least) 

 as starch, without conver 

 sion into dextrin or sugar, 

 as these substances do not 

 appear in the cotyledons during any period of germina 

 tion, except in small quantity near the joining of the 

 seedling. Compare p. 64, Unorganized Starch. 



The same authority gives the following account of 

 the microscopic changes observed in the starch-grains 

 themselves, as they undergo solution. The starch-grains 

 of the bean hive a narrow interior cavity, (as seen in 

 fig. G5, 1.) This at first becomes filled with a liquid. 



Fig. 65. 



