1 8 The Heterogony of Oxalis violacea. [January, 



portion of the anthers are of a white color and quite destitute of 

 pollen ; others which are pale yellow contain many bad with 

 some good grains ; and others again which are bright yellow 

 have apparently sound pollen; but he has never succeeded in 

 finding any fruit on this species. The stamens in some of the 

 flowers are partially -converted into petals. Fritz Miiller after 

 reading my description * * * of the illegitimate offspring 

 of various heterostyled species, suspects that these plants of 

 Oxalis may be the variable and sterile offspring of a single form 

 of some trimorphic species, perhaps accidentally introduced into 

 the district, which has since been 'propagated asexually." A case 

 somewhat similar to that of Oxalis violacea about Madison, is 

 afforded by a Brazilian species of Pontederia, of which Fritz 

 Miiller 1 found only long and short-styled flowers. An important 

 difference, however, is found in the measurements of the pollen 

 from the different sets of stamens of a given flower; for "the 

 pollen grains distended with water from the longer stamens of the 

 short-styled form are to those from the shorter stamens of the 

 same form as ioo to 87 in diameter, as deduced from ten meas- 

 urements of each kind. * * * Moreover, the longer stamens 

 of the long-styled # form of Pontederia, and the shorter ones of 

 the short-styled form are placed in a proper position for fertilizing 

 the stigma of a mid-styled form." 



" With respect to the absence of the mid-styled form in the case 

 of the Pontederia which grows wild in Southern Brazil," Mr. Dar- 

 win adds, " this would probably follow if only two forms had been 

 originally introduced there; for, as we shall hereafter see from 

 the observations of Hildebrand, Fritz Miiller and myself, when 

 one form of Oxalis is fertilized exclusively by either of the other 

 two forms, the offspring generally belong to the two parent- 



Whether in 0. violacea we are dealing with a case of this sort, 

 or whether the species is dimorphic, can only be definitely decided 

 by the examination of many specimens collected over as large a 

 range of territory as possible, and it is to be hoped that those 

 who have the opportunity will make observations of this sort. 

 Meantime it seems not improbable that the plant is dimorphic ; 

 and although dimorphic species are as yet unknown in this genus, 



1 Jenaische Zeitschr., VI, 1871, p. 74, fide Darwin. 1. c, p. 184. 



