12 GERMINATION OF THE SEED. CHAP. I. 



radicle only is developed.* Senebier found also 

 that seeds will not germinate in an artificial atmos- 

 phere that does not contain at least one eighth part 

 of its bulk of oxygene ; but that the most favour- 

 able proportion is when it contains one fourth 

 part.'f- It has been ascertained, however, that seeds 

 will germinate even in an atmosphere of pure 

 oxygene, though not so readily as when presented 

 in a state of mixture or combination with other 

 gases. It cannot indeed be necessary that the 

 oxygene consumed in germination should be pre- 

 sented to the seed in an uncombined state ; as is 

 obvious from the natural agency of the atmospheric 

 air, as well as from direct experiment. Humboldt 

 found that the process of germination is accelerated 

 by means of previously steeping the seed in water 

 impregnated with oxy muriatic acid.^ Cress-seed 

 treated in this manner germinated in the space of 

 three hours, though its ordinary period of germi- 

 nation is not less than thirty-two hours. The ex- 

 periment was afterwards repeated by Saussure, with 

 a similar result ; and may be regarded as perfectly 

 correct. Thus it is known that this acid parts very 

 readily with its oxygene. The cause, then, of the 

 rapid germination of the Cress-seed is obvious ; and 

 the proof that the oxygene does not require to be 



* Saussure sur la Vcg. 



f Mem. sur 1'Influ. de 1'Air, Nich. Journ. 1801 



I Journ, de Phys. xlvii. p. 63, 



