THE FUNCTIONS OF ROOT-HAIRS. 49 



it also, or it may take it up and fix it, or break it 

 up or otherwise alter it. 



More recent researches, and especially those of 

 Pfeffer, have shown that these diosmotic properties 

 of the living protoplasm are of the utmost 

 importance in the whole matter of absorption of 

 substances from the soil. 



Let us suppose the following case. A root- 

 hair, in full vigour, is allowed to bathe freely in 

 a dilute solution of various substances, such as 

 sugar, potassium nitrate, phosphates, sulphates and 

 carbonates of iron, soda, lime, magnesium and 

 others known by experiment to be harmless to its 

 life. 



Now it turns out to be by no means a foregone 

 conclusion that all or any of the substances, even 

 though freely soluble in the water, can pass 

 through the protoplasm into the interior of the 

 cell. Some may be allowed easy access, others 

 may only be permitted to pass in small quantities, 

 and others, again, may be absolutely refused 

 access by the delicate living filter, so long as it 

 is vigorously alive. Nor, as proved by numerous 

 experimental cultures since De Saussure's time, is 

 the entrance of a salt, etc., ruled by its indispensa- 

 bility or otherwise in the economy of the plant. 

 And it is important to notice that only experiment 

 can prove the point and determine which sub- 

 stances are absorbed and which refused by the 

 root-hair. 



If we now suppose the protoplasm to give rise 

 to powerfully osmotic substances which accumulate 



D 



