A^TMOSPIlEnK' AIR AS THE FOOD OP PLANTS. 



23 



tlon, viz.: in germination. We know that the presence of 

 oxygen is an indispensable requisite to the sprouting seed, 

 and is possibly the means of provoking to action the dor- 

 mant life of the germ. The ingenious experiments of Traube 

 (H. C. G., i\ 326.) demonstrate conclusively that free 

 oxygen is an essential condition of the growth of the 

 seedling plant, and must have access to the plumule, and 

 especially to the parts that are in the act of elongation. 



De Saussure long ago showed that oxygen is needful to 

 the development of the buds of maturer plants. He ex- 

 perimented in the following mamier : Several woody twigs 

 (of willow, oak, apple, etc.) cut 

 in spring-time just before the 

 buds should unfold were placed 

 under a bell-glass containing 

 common air, as in fig. 1. Their 

 cut extremities stood in water 

 held in a small vessel, while the 

 air of the bell was separated 

 from the external atmosphere by 

 the mercury contained in the 

 large basin. Thus situated, the 

 buds opened as in the free air, 

 and oxygen gas was found to be 

 consumed in considerable quan- Fig. 1. 



tity. When, however, the twigs were confined in an 

 atmosphere of nitrogen or hydrogen, they decayed, with- 

 out giving any signs of vegetation. {Reeherches sur la 

 Yegetatioii, \). 115.) 



The same acute investigator found tliat oxj'^gen is ab- 

 sorbed by the roots of plants. Fig. 2 shows the arrange- 

 ment by which he examined the effect of difierent gases 

 on these organs. A young horse-chestnut plant, carefully 

 lifted from the soil so as not to injure its roots, had the 

 latter passed through the neck of a bell-glass, and the stem 

 was then cemented air-tight into the opening. The bell 



