394 



LECTURE XVI. 



The numbers represent millimetres. 



Von Wolkoff made similar observations on the roots of 

 seedlings of Pisum sativum. 



Twelve seedlings were measured in each case, and the period of 

 growth was 5 days. The measurements are in millimetres. 



In the dark. Under normal conditions. 

 Total elongation 923 7 1 5 



The effect of light in retarding the rate of growth in length 

 makes itself evident even after a short exposure. This is 

 strikingly shewn by the results of some experiments which I 

 made with the yexaet sporangiferous hyphae of Phycomyces 

 nitens. These delicate filaments are upgrowths of the much- 

 branched tubular cell which constitutes the mycelium of this 

 plant. The plant was grown in darkness and was exposed at 

 intervals to light. 



The following are the measurements made at intervals of an hour 

 upon a hypha. 



* Exposed to light. 



The figures correspond to j^s of a millimetre. 



