no 



count a perfectly superficial sowing of the seed would be advisable if periods 

 did not occur in spring which dry up the surface of the soil to such an ex- 

 tent that a temporary or even a permanent inhibition of the life activity takes 

 place in the seedling. 



The more porous the soil, the greater is the danger of drying out and 

 therefore the greater the depth at which the seed must lie. In regions where 

 the spring is dry a heavy soil will give a more uniform germination even if 

 the sowing is shallow. The same soil and the same depth of sowing become 

 dangerous when strong rainfall and great heat alternate rapidly and form 

 crusts on the upper surface of the soil cutting off nearly all access of air to 

 the seeds then in a most active stage of metabolism. The air enclosed in the 

 seeds does not last long. Ventilation of the plant body is, however, absolute- 

 ly necessary, even the germinating seed sufil'ers extremely if the air contained 

 in it be removed. The formation of heavy crusts on the soil can make the 

 depth of sowing of the seed become the cause of consideral'ly injury, which 

 in itself would not be injurious. 



How much the lack of air influences the germination rapacity of seeds 

 is evident from de Vries^ citations. In this connection Haberlandt injected 

 curly beet seeds with water under an air pump and observed that the seeds 

 took up 71.13 per cent. ; of these seeds thus partially deprwed of air only 30 

 per cent, germinated as against 90 per cent, of the normal seeds kept as a 

 control. In a second experiment all the air was replaced by water forced in 

 by the air pump and only 8 per cent, germinated as against 72 per cent, in the 

 control. 



Also the time required for germination was shorter in the normal seeds. 

 It may well be assumed that the removal especially of oxygen from the seed 

 and the hindered diffusion of this gas in new quantities into the intercellular 

 spaces is the cause of the loss in germinating power. Dutrochet- 

 found even in mature plants that death often occurs if water is injected. In 

 the rapid thaivimj of frozen fleshy parts of plants which, as a result of an 

 infiltration of the intercellular spaces with water, have a glassy, translucent 

 appearance, the exclusion of the air from the cells by water may contribute 

 essentially to their death. 



From the many experiments carried out practically in order to obtain 

 precise numerical values, for the best depth for sowing seeds, those of Roes- 

 tell, Tietschert, Ekkert and Wollny are the most thorough. Roestell" 

 gives 2 to 4.5 cm. as the most favorable depth for porous, strong, field soil. 



Tietschert* experiments endeavor to determine the maximum boun- 

 daries of the most favorable seeding depths in soils differently con- 

 structed physically; — 10 cm. was seen to be the rational maximum depth for 



1 De Vries, Keimun,?s£reschichte dcr Zuckerriibe, Landwirtsch, .Tahrb. v. Thiel 

 1879, p. 20. 



2 Dutrochet, Memorires etc. edition Bruxelles p. 211, cit. by de Vries 1. c. 



3 Annalen der Landwirt.schaft, Vol. 51, p. 1. 



* Tietschert, Keimungsversuche mit Roggen and Raps. Halle. 1871. 



