LINNAEUS AS AN EVOLUTIONIST 87 



folia. They are very peculiar plants, uncom- 

 monly interesting from several points of 

 view, and have in recent years profoundly 

 engaged organographers and physiologists; 

 but Linnseus was most interested in their 

 ecology as bearing upon the problem of their 

 genealogy. Both are bog plants, though far 

 enough from being found in every northern 

 bog. They seem to be particular about the 

 kind of soil, the amount of moisture, the nature 

 of the exposure, and also the plant associates 

 amid which they will establish their habita- 

 tion; and both species are at perfect agreement 

 as to all special details of bog environment 

 which they demand; for where one is found, 

 there too is the other. They are much alike 

 in size, mode of growth, degree of hariness, 

 form and color of flowers, etc., but the leaf 

 blades in one are round, while in the other 

 they are so much elongated as to be called 

 narrowly oblong; and this one strong dis- 

 tinguishing mark is constant. There are no 

 plants among them to show leaves intermediate 

 between orbicular and oblong. They ought 

 to be, and I think that by all botanists except 

 LinnaBUS, both before his day and ever since, 

 they have been held distinct; and even he did 

 not positively affirm the contrary, but only 



