CH. II.] THE ROOT. Ill 



benefit accruing to cultivated plants from animal and 

 vegetable manures decomposing in the soil ; but they 

 do more, for they afford additional evidence to that 

 already given, how erroneously those persons argue 

 who recommend the seed to be soaked in powerfully 

 stimulating manures, for no other reason than because 

 they are grateful to the adult plant. Carbonic acid gas, 

 though an efficient promoter of a plant s growth when 

 mature, is a check to its progress whilst the root ls 

 forming. Saussure placed peas so that their just deve- 

 loped radicles were immersed, some in distilled water, 

 and others in water impregnated with carbonic acid. 

 The radicles when the experiment commenced were 

 two lines and a half in length, and in ten days those 

 in distilled water were five inches longer than those 

 in the acidulated water, and the stalks and leaves 

 were equally superior. But when a month had 

 passed, the relative superiority was reversed, and in 

 six weeks the plants fed with carbonic acid were in 

 eveiy respect most vigorous. Ruckert obtamed 

 nearly the same result when beans were grown in 

 earth, some being watered with distilled water, and 

 the others mth water impregnated with carbonic 

 acid. 



Every farmer, in districts where marl is to be 

 obtained, is aware that it is highly beneficial when 

 applied to the land ; few of them, however, know, that 

 this various-coloured compound of earths contains 



