104 ON THE FOOD OF PLANTS. 



" sition, it may not be distinctly found in them, 

 " or, at least, not distinguished from that newly 

 " formed, during their decomposition." 



He also says, '* The agency of water, in the 

 " process of vegetation, has not till of late 

 " been distinctly perceived. Dr. Hales has 

 " shown, that in the summer months, a sun- 

 " flower, weighing three pounds, avoirdupois, and 

 *• regularly watered every day, passed through 

 *' it, or perspired, twenty- two ounces each day j 

 " that is, half its weight. 



*' Dr. Woodward found that a sprig of com- 

 " mon spearmint — a plant that thrives best in 

 " moist soils, weighing only 28.25 grs., passed 

 *' through it SOO^ grs. in 77 days, between July 

 ** and October, that is, somewhat more than 

 *' its whole weight each day ; he did more, for 

 " he found that in that space of time, the plant 

 *' increased 17 grs. in weight, and yet had no 

 " other food but pure rain water ; but he also 

 " found that it increased more in weight when it 

 ** lived on spring water, and still more when its 

 '* food was Thames water. Secondly, that the 

 " water they thus pass, nourishes them merely 

 *' as water, without taking any foreign substance 

 *' into account; for 3000 grs. of rain water, in 

 " Dr. Woodward's experiments, aflbrded an in- 

 *' crease of 17 grs. : whereas, by Margraaf's ex- 



