52 



direct impact of the waves. There are several sorts of forces 

 thus brought to bear upon the sea palm. The waves may strike 

 the plant at right angles to the long axis, they may tend to crush 

 the plant to the surface of the rock by their great weight, or they 

 may exert a pulling force. And the plant has become a sort of 

 living resultant of these forces. 



To compare the two kelps with regard to the mechanical 

 strength, I applied to the sea palm the same sort of blow that 

 had been previously given to the bladder kelp. The result was 

 what one would expect ; it did not have the slightest effect. In 

 addition, I found it quite impossible to wrench the kelps from 

 their station, however hard I might try. 



Briefly, it would appear then that the differences of the sea 

 palm and the bladder kelp in habitat, more especially the dif- 

 ference in their exposure to the waves, go far to explain the dif- 

 ferences which the plants themselves exhibit as regards me- 

 chanical strength, and, further, these plants appear to be able to 

 withstand those stresses best which also occur among the condi- 

 tions of their environment. 



Columbia University. 



THE NORTH AMERICAN TWINFLOWERS 



By P. A. Rydberg 



In all our manuals of botany, Linnaea is given as a monotypic 

 genus, consisting of only L. borealis L. One variety has, how- 

 ever, been recognized by some botanists, viz., L. borealis var. 

 longiflora Torr. , described from the collection made on the Wilkes 

 Expedition. This is found in the extreme eastern portion of Asia 

 as well as on the American Pacific Coast from Alaska to Cali- 

 fornia, and extends also into the Rocky Mountain region in British 

 Columbia and Idaho. In connection with my work on the flora 

 of the Rockies, I happened some time ago to look up the record 

 of this plant. As a rule, it is easily distinguished from the com- 

 mon twinflower of the East and of the Rockies by its much 

 longer leaves, especially on the flowering branches. In depau- 



