464 



THE SEED AND ITS GERMINATION. 



1204. The greater part of the increase in weight and volume 

 from the absorption of water bj' dry seeds takes place in a short 

 time ; for example : — 



After this there was very little gain either in weight or volume. 



1205. Access of free oxygen must be provided to secure 

 germination. Even if all other conditions are favorable, germi- 

 nation does not take place in pure water devoid of any free 

 oxygen, or in an atmosphere of nitrogen. 



1206. The oxygen accessible to the seed must be diluted to 

 about the degree found in common atmospheric air, although it 

 is not necessary that the dilution should be made with nitrogen, 

 as is the case with air. Boehm ^ has shown that a mixture of 

 proper proportions of hydrogen and oxj'gen answers about as 

 well as a mixture of nitrogen and oxygen for germination of 

 seeds, provided it is furnished to them under ordinary atmos- 

 pheric pressure. That the degree of pressure is an important 

 factor, is proved by Bert's'' experiments. Barley gave the 

 following results : — 



Percentage germinated. 



In ordinary air (76 cm. pressure) 84 



In air 50 " " ... • • • ^^ 



25 " " ; ; 28 



6 " " 10 



The proportion of oxygen to nitrogen in atmospheric air is 

 approximately 1 : 5 (oxygen, 21, nitrogen, 79 parts). 



1207. The temperature requisite for germination to begin 

 differs considerably in different species. The lowest tempera- 

 ture recorded is the following, noted by Uloth : « In a perfectly 

 dark ice-cellar seeds of Acer platanoides sprouted on ice, the 

 rootlets penetrating to a depth of 5 to 7.5 cm. into the dense 



1 Sitzbev. : Wien Akad., Ixviii., 1873, p. 132. 

 ^ Comptes Eendus, Ixxvi., 187,5, p. 1493. 

 ' Flora, 1871, p. 185. 



