182 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



POLYMORPHISM or ALGIE. 



Klebs and other workers found that many green algse 

 were capable of existing in two or more forms, but the 

 stimulus inducing the change was unknown. It remained 

 for Livingston (1900) to show that this was of a simple 

 nature, being none other than the osmotic pressure of the 

 solution in which the algae grew. 



Livingston demonstrated that the responses of Stigeo- 

 clonium (tenue ?), both in form and in reproductive activity, 

 which accompany a change in concentration of the Knop's 

 solution in which it is growing, are due to changes in the 

 osmotic pressure of the medium, and are in no way func- 

 tions of its chemical composition. Further work (1901) 

 established the fact that solutions of non-electrolytes pro- 

 duce the same result as those of electrolytes, for in them, 

 too, osmotic pressure is the controlling factor in deter- 

 mining the form of the plant. This is effective through 

 changes in the water content of the cells. 



It should be mentioned that this species of Stigeo- 

 clonium grows on moist bark, and there exhibits the 

 palmella form. The spherical cells multiply by division 

 in vertical planes at right angles to each other, the daughter 

 cells separating more or less completely after division. In 

 the filamentous form the cells are cylindrical and remain 

 in contact; division takes place in transverse planes. 

 Both forms effect reproduction by means of comparatively 

 large asexual biciliate zoospores. 



In addition, Livingston found that a high osmotic 

 pressure* affects the plant in four ways: (a) It decreases 

 vegetative activity; (b) it inhibits the production of 

 zoospores ; (c) it causes cylindrical cells to become spherical ; 



* The highest osmotic pressures employed by Livingston in these 

 researches only slightly exceeded 8 atmospheres at 0. 



