OSMOTIC PRESSURE IN RELATION TO PLANT DISTRIBUTION 183 



(d) it frees the alga from certain limitations as to the 

 orientation of the planes of cell division. Conversely, a 

 low pressure reverses these effects. It was also ascer- 

 tained that there were certain quantitative differences be- 

 tween the concentrations required to inhibit zoospores in 

 the palmella and in the filamentous stage, those required 

 for the former being the greater. Between the behaviour 

 in this respect of electrolytes and of non-electrolytes, such 

 as sucrose, quantitative differences were found. These 

 are all explicable on the assumption that the permeability 

 of the cells is greater towards the latter. Furthermore, 

 it was proved that prolonged darkness does not induce a 

 change in the form of the alga. 



That all these phenomena are due merely to variations 

 in the amount of water in the vacuoles appears very im- 

 probable. It seems more reasonable to connect them with 

 alterations in the state of imbibition of the protoplasmic 

 colloids ; also with changes in the rate of oxidations which 

 normally occur in the cell, owing to increases or decreases 

 in the area of external surface, and consequent disturbance 

 of the usual rate of intake of atmospheric oxygen. The 

 loss of their motility experienced by many bacteria when 

 brought into solutions of a high osmotic pressure appears 

 to be a quite similar instance of disturbance caused by 

 the withdrawal of water from the protoplasm, for bacteria 

 are very freely permeable to most salts. Wladimiroff 

 (1891) has employed this arrest of the activity of motile 

 bacteria to measure osmotic pressures. 



POLYMORPHISM OF FUNGI AND STRUCTURAL CHANGES 

 IN ANGIOSPERMS. 



Beau verie (1900, 1911) has studied the growth of various 

 fungi, such as the Mucorinae and the conidial forms of the 

 higher groups, in solutions of different concentrations. 



