142 



The Ottawa Naturalist. 



[Feb. 



Compared Size of 

 P. racemosa, P. trifoliata, P. mainensis. 



The series of specimens is not numerous enough to show 

 very clearly a curve of Quetelet, but what stands prom'nently 

 is the fact that P. mainensis, the hybrid, is taller by 63 per cent, 

 than the parent species (figuring on the means). What are the 

 causes of this increased luxuriance? They are yet a matter of 

 research. Tischler and Jost (*) agree that it is probably due 

 to a "poisoning" effect of one species on the other. 



Leaves. 

 We have not been able to see the radical leaves of P. main- 

 ensis of which Gray makes so much in the above-mentioned 

 description, but we observe that the lowest stem leaves taper 

 into a winged petiole which sometimes reaches 10 cm. Most re- 



*"Arch.ZelIsforchung," I., 33-151, 1908. 



