74 ROOTS. [CH. Ill 



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 {Nasturtium 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 

 700 c.c. of a solution made by dissolving 1 part of 

 potassium chloride in 1000 parts of water. They were 

 left in the fluid for 8 days, by which time only 260 c.c. 

 of solution were left in the beaker. This was ana- 

 lysed volumetrically, by titrating with decinormal silver 

 nitrate, using potassium chromate as indicator. If the 

 salt and the water had been absorbed in the same 

 proportion the remaining solution should have still con- 

 tained O'l p.c, i.e. 0'26 grams ; in other words, the plant 

 should have absorbed 0"44 grams. It was found however 

 that less than this had been taken up, and that f, i.e. 

 O'o grams, of the original potassium chloride instead of 

 0*26 grams were still present. Other salts give various 

 different coefficients for this same strength of solution. 

 If sufficiently dilute solutions be made use of, it has 

 been found that, in contrast, relatively more salt than 

 water is absorbed and the remaining portion of the liquid 

 contains less than the due proportion of the original salt. 



(88) Root pressure. 



Root pressure can be easily observed in young plants of 



