1922] 



PAYSON — STUDY OF THELYPODIUM AND ITS IMMEDIATE ALLIES 23 



made of differences in the septum to distinguish the species, but 

 as a generic character the pattern is of great importance. No spe- 

 cies are now admitted to Thelypodium that do not exhibit this 

 type of septum. There are, however, species outside the genus 

 that have apparently developed a similar type independently. 



It would be difficult to trace any developmental series in the 

 character of the septum, but it is of some interest to notice that 

 in T. laciniatum, which has been found primitive in at least two 

 respects, the cell-walls in the middle region are not so closely 

 compacted as in certain other species. The septum of T. eucosum 

 is not known. 



Seeds. — As far as present studies show, the seeds in this genus 

 are very uniform and furnish no characters of taxonomic or phy- 

 logenetic importance. In common with related genera the posi- 

 tion of the radicle in the species of Thelypodium is almost in- 

 variably oblique with reference to the cotyledons. Occasionally 

 the seeds are slightly pointed or apiculate but are never winged 

 or conspicuously margined. 



The flowers. — In common with most of the members of this 

 family the flowers of Thelypodium do not exhibit much variation. 

 Only two points need be considered here, the shape of the petals 

 and their color. In shape they vary from narrowly linear, as in 

 T. stenopetalum, to broadly oblanceolate, as in T. flexuosum. 

 Since neither of these species is primitive as to length of stipe 

 or pod it seems probable that neither of these two extremes rep- 

 resents the ancestral type for the genus. Rather we would be in- 

 clined to suppose a broadly linear or long-spatulate form more 

 nearly like the original, since it occurs in T. laciniatum, T. euco- 

 sum, and certain other species that seem primitive in other re- 

 spects. Within the genus the petals are never conspicuously 

 crisped or channeled as in Caulanthus; they are always entire 

 and there is rarely any differentiation between blade and claw. 



In color the petals of the various species range from red-pur- 

 ple to blue and white. No species with yellow petals is known. 

 T. laciniatum has white petals, and T. eucosum has red-purple 

 ones. Within specific limits the range in color is often extreme, 

 as in T. lilacinum in which the petals vary from deep purple to 

 white. There is indication, however, that the color forms are 

 more or less isolated geographically and therefore the variation 

 may have its phylogenetic significance. The form of that spe- 

 cies that occurs in the eastern part of its range seems to be al- 

 most entirely white. 



