109 



THE FRUIT OF TROPIDOCARPUM. 

 By B. L. Robinson. 



No genus of North American Crucifei^ce presents such 

 peculiar difficulties in its specific subdivision as Tropidocar- 

 pum. The vegetative characters of stature, degree of branch- 

 ing, division of leaves, &c., as in most annuals of this order, 

 are highly variable and so evidently influenced by the indi- 

 vidual environment as to be thoroughly unsatisfactory as 

 specific distinctions. Nor have the inflorescence and floral 

 envelopes yielded any good basis for the separation or limita- 

 tion of species. It is true the pedicels vary somewhat in 

 length and curvature. The petals are sometimes golden yel- 

 low, more often pale yellow, and sometimes salmon-colored 

 or even roseate. The sepals are hirsutulous or sometimes 

 smoothish. Yet here as in the foliage the variation appears 

 to be gradual and of the formal sort, in which each member 

 is modified independently of every other. 



With the fruit, however, the variations are more consider- 

 able and the differences (at least at first sight) appear to be 

 those of kind rather than degree. The critical investigation 

 of these differences is of much importance in estimating the 

 value of the existing species, and indeed some of the cap- 

 sules form such noteworthy exceptions to the general fruit 

 structure of the order, that, quite apart from their immediate 

 systematic bearing, they merit detailed description. It is 

 impossible with the limited material at hand to treat the sub- 

 ject as thoroughly as it deserves, yet it is hoped that the 

 present notes may draw attention to the peculiar anomalies of 

 the group and that some one so situated that he can make 

 field studies or cultures may continue the observation of the 

 genus. Besides the material in the Gray Herbarium, the 

 writer has been permitted to examine the entire representa- 

 tion of Tropidocarpum from the Herbarium of Columbia 

 College, the California Academy of Sciences, and the Her- 

 barium of the University of California, and for this privilege 

 wishes here to express his cordial thanks to Prof. Britton, 



Erythea, Vol. IV., No. 8 [7 August, 1896]. 



