66 BOOTS. [CH. Ill 



grown under wooden frames covered with fine netting (mesh 

 l-o mm.) to exclude insects. The fed plants soon begin to 

 look clearly greener and more vigorous than the unfed 

 ones. To get a good result the experiment should be 

 begun in May or June and continued to the middle of 

 August. The number and height of the flower scapes, 

 the number and weight of capsules, the number of seeds 

 per capsule, &c. should be compared. Or the plants may 

 be carefully washed and dissected out of the moss and the 

 dry weight per plant of the fed and starved specimens 

 compared. 



Section C. Roots. 



(87) -De Saussure's experiment^. 



When plants are placed in solutions of various salts 

 they do not, except under certain conditions, absorb the 

 water and salt in the same proportion. De Saussure, 

 using solutions that were not very dilute, found that the 

 plant absorbed a relatively less salt than might have been 

 expected. This condition of things is sometimes spoken 

 of as absorption according to De Saussure's law, and 

 although it is well known to be only a special case, the 

 fact itself is worth confirming. In our experiments we 

 proceeded as follows. 



A bunch of rooted water-cresses {Nastwrtiwm officinale) 

 was taken up, washed and placed in distilled water for 

 three days to allow the roots to recover from their in- 

 juries. They were then placed in a beaker containing 

 1 De Saassaia, Recherches chimiques, 1804, p. 247. 



