CELLULAR ANATOMY OF THE ROOT 



231 



living cells) is impervious to the sugar solution. Another 

 difference between them is that the membrane opens into an 

 open tube, while the root hairs do not, but communicate 

 through lines of living cells with the ducts in the root and 

 stem. How the water gets from the hairs unto these ducts 

 is as yet entirely unknown. But the primary physical process 

 is the same in the parchment cup and the living root-hair 

 cell, and in Experiment 9 one may say that on the one side 

 we have a great number of tiny hairs, and on the other 

 a single gigantic one. 



Experiment No. 9. Take two 

 burettes of 16 mm. diameter, and 

 remove the bottom up to 2 cm. 

 below the beginning of the gradu- 

 ation, and smooth the cut end in 

 the flame. Over one of them fit 

 a soaked diffusion shell of 16 mm. 

 diameter (which may be obtained 

 of Eimer and Amend of New 

 York), and tie it to the burette 

 very tightly with a waxed thread. 

 Fill it with a thin solution of 

 molasses up to the zero mark. 

 Such an instrument is a very effi- 

 cient osmometer. The molasses 

 may be made stronger if quicker 

 working is desired. These shells 

 are the best arrangements for the FIG. 23. -Osmometers constructed 



purpose I know of, but if they are from a parchment shell and 

 ill r j from a living plant, xl. 



not available, a piece of good 



parchment (generally obtainable of bookbinders) may be soaked 



and stretched tightly over the lower end of the burette ; of 



