CH. Ill] ROOTS. 67 



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. 026 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 ^, i.e. 

 0'5 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 sohxtions 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. 



Eoot pressure can be easily observed in young plants of 

 Phaseolus. An indiarubber tube T (Fig. 11) is tied on the 

 cut stump, S, of the plant and is filled with water : a capil- 

 lary glass tube G is tied into the tube, leaving about six 

 centimeters of rubber tube full of water between the 

 stump' and the bottom of the glass tube. The glass tube 

 is now fixed in a clip and after a time drops of water fall 

 fi"om the end E. To get an idea of the rate of flow it is 

 only necessary to gently pinch the rubber tube so as to 

 press the fluid out, and to absorb it with filter-paper held 



5—2 



