28 



THE WHEAT PLANT 



PERCENTAGE GERMINATION 



At temperatures considerably above the optimum the grains 

 germinate irregularly, the sprouting of some of them being much delayed. 

 Moreover, the embryos frequently die or become so much weakened that 

 they are liable to be destroyed by the attacks of fungi and bacteria ; the 

 endosperm also often undergoes decomposition through the activity of 

 these organisms when the moist grains are kept at 35 C. or higher. 



Although germination begins in two or three days or less in grain 

 sown in the open field at any period of the year, the progress made by the 

 growing embryo is very slow in late autumn and winter when the tem- 

 perature is low, especially if at the same season the rainfall is excessive. 

 The time which elapses before the coleoptile appears above ground in 

 grains deposited at a depth of an inch may vary between one and ten 

 weeks. 



Observations made upon weekly sowings of wheat during 1912, 1913, 

 and 1914 gave the following results, the grains being sown at a depth 

 of one inch : 



NUMBER OF DAYS BETWEEN THE TIME OF SOWING AND THE APPEARANCE 

 OF THE YOUNG PLANT ABOVE GROUND IN WHEAT SOWN IN DIFFERENT 

 MONTHS OF THE YEAR. 



During germination extensive chemical changes occur both in the 

 embryo and the reserve materials of the endosperm. 



Starch is absent from the tissues of the dormant embryo except in the 

 merest traces, but minute globules of a fatty oil and small spherical aleuron 



