438 



Plant Physiology 



species of seed-plants ; that is to say, many fungi and bac- 

 teria may grow in solutions which would inhibit root 

 growth. However, aerial surfaces of seed-plants do not, 

 as a rule, permit the. rapid absorption of water or of chemi- 

 cal agents, so that for crop protection such surfaces may 

 be covered with strengths of toxic solutions prohibitive 

 to the germination and growth of fungi, as in the use of 

 fungicides and insecticides. 



FIG. 124. Depression of toxicity with addition of sand. [After True 

 and Oglevee.] 



