No. 520] 



EVOLUTION IN VIOLA 



yellow, two generations of offspring from the Mulford 

 plant show the black color to be stable. 



Just the opposite effect has been brought to pass in cer- 

 tain plants of V. neplirophylla, a northern species rang- 

 ing from eastern Quebec to the Rocky Mountains, and 

 having black seeds in all the many specimens seen, ex- 

 cept the one here discussed. This plant with buff seeds 

 appeared in a parcel of V. neplirophylla sent from Lake 

 Nemahbin, Wis., in 1907, by Dr. Ogden, of Milwaukee. The 

 plant was in all other characters good V. neplirophylla; 

 the capsules were crowded with seeds which for two gener- 

 ations have in turn produced plants with like buff seeds. 

 Now from the same region Dr. Ogden sent me a few days 

 later the hybrid V. afjinis X neplirophylla, seeds from 

 which the following year gave plants with buff as well as 

 with black seeds. It is therefore probable that the fertile 

 and stable buff-seeded V. neplirophylla from Lake Ne- 

 mahbin is the descendant of a hybrid of this species with 

 buff- seeded V. a finis. 



Many similar cases have come under observation. In 

 a limited region in Salisbury, Vt., of less than a square 

 mile, there occurs not infrequently a very pubescent form 

 of V. latiuscula, a species which in all other stations I 

 have found to be quite glabrous. On the other hand, 

 from three stations I have obtained perfectly glabrous 

 plants of V. palmata, a species normally pubescent. The 

 plants from two of these three stations were somewhat 

 infertile, thus betraying their hybrid origin. 



The effect of hybridism is plainly to be seen in the nu- 

 merous intergradient forms that occur between closely al- 

 lied species of Viola. Take, for example, V. fimhriatula 

 and V. sagittata, merged into one species by Dr. Gray, 

 probablv because of this intergradience. The extreme 

 forms differ chiefly in three particulars: the leaf-blade of 

 V. sagittata is narrowly lanceolate, glabrous and coarsely 

 toothed at the base; that of V. fimhriatula is oblong-lan- 

 ceolate, pubescent and not coarsely toothed at the base. 

 But not infrequently we find colonies of Viola fimhriatula 



