1886.] 297 [Trelease. 



Thalictrum petaloideura and other foreign species are as markedly 

 entoraophilous as Anemonella and Anemone. Of our own species, 

 T. clavatum and T. sparsiflorum are unquestionably adapted to in- 

 sect-pollination. The former has small stigmas, included stamens, 

 small anthers and relatively conspicuous flowers. The latter, with 

 inconspicuous flowers and longer filaments and stigmas, approaches 

 an anemophilous condition that is intensified in T. polygamum, 

 which has dilated, rigid and conspicuous filaments and short 

 anthers, but more numerous stamens and large stigmas, so that it 

 is adapted to either insect- or wind-pollination. T. purpurascens, 

 with more strictly dioecious flowers (those of the fertile plants, 

 therefore, less ornate, and rarely tempting insects by a provision 

 of pollen), longer and more flexuous stamens and larger anthers, 

 with a superabundance of pollen, departs still more from the ento- 

 mophilous type, and is apparently mainly dependent upon the 

 wind. Our other species appear to be exclusively anemophilous. 

 Connected with these floral differences, a difference in the pollen 

 of the extreme forms might have been expected, but the examina- 

 tion of dried specimens shows that no such difference exists, the 

 pollen grains of all being nearly globose and smooth, and differ- 

 ing only to a limited extent in the unimportant character of size. 

 Persons who have the opportunity should observe whether all of 

 our hermaphrodite species are protogynous, as T. minus is said to 

 be by Miiller. 1 



It is interesting to note in connection with the prevalence of 

 anemophilous and dioecious flowers, that our species are all en- 

 demic except T. alpinum, which, like many arctic-alpine species, oc- 

 curs on both continents ; T. minus, a European and Siberian species, 

 one variety of which has barely reached the new world by way of 

 N. E. Asia ; and T. sparsiflorum, which, reaching this continent in 

 the same way, has extended southward in the mountains, like the 

 first. 



The following arrangement of the species which belong to the 

 Flora of North America shows their essential characters, and, to 

 a certain extent, their relationship : — 



* Flowers all perfect. 

 Stigma minute ; filaments short, broad and petaloid above, 



— T. clavatum. 



!Fert. of Flowers, 71. 



