46 FIELD MUSEUM OF NATURAL HISTORY BOTANY, VOL. IV. 



A comparison of Wallroth's Latin description with the others in his 

 monograph shows two outstanding features for his X. oviforme. The 

 fruits were very large and were covered with strong, horn-shaped prickles, 

 these densely clothed at their base with jointed, reddish hairs. Further- 

 more, Wallroth based his species directly upon Hooker's Xanihium 

 canadense from North America ("X. Canadense Hook, in lit. (herb, 

 general berol.), nee Herm., Mill, et Linn. Angeblich in Nordamerika 

 und vermuthlich in Canada."). 



Thus, Wallroth had seen a plant in Berlin labeled "X. canadense" 

 by Hooker, but which appeared distinct from all other specimens 

 because of its mammoth burs and their horn-shaped prickles. On 

 reference to Hooker's Flora Boreali-Americana, a work published in 

 1840 and which Wallroth appears not to have seen, we find the basis of 

 Wallroth's species. Hooker (loc. cit. 308), instead of giving an extended 

 range or list of stations as in the case of many other species, gave 

 merely, "Hab. Canada? North-West coast of America. Douglas." 

 So the plant determined by Hooker as X. canadense was a plant collected 

 by Douglas along the northwest coast of (North) America. 1 But it was 

 in this same region that the type of X. silphiifolium Greene was ob- 

 tained. Greene's type was collected by Suksdorf, on the banks of the 

 Columbia River, 2 September, 1883. While this type itself (in Hb. U. S.) 

 is at present inaccessible to us, we have seen the two excellent cotypes 

 in the Herbarium of Field Museum and also the two other specimens 

 by Suksdorf in Gray Herbarium. These all agree well with each other 

 in having large, coarse burs, with very strong, elongate, reddish-hispid, 

 horn-shaped (arcuate), hooked prickles and somewhat similar beaks; 

 the lower prickles on each bur tend to be strongly grooved upon the 

 ventral face. The specimen collected by Suksdorf on bottom lands of 

 the Columbia River (no. 189) is particularly instructive. It is accom- 

 panied by one mature bur, much larger than the rest, a bur such as 

 most collectors might shrink from trying to press. This bur is really of 

 gigantic proportions, having a size observed by us so far in only two 

 other species (X. campestre and X. speciosum). The body proper is 

 2.3 cm. long and about i cm. thick. The prickles and beaks measure 

 from 8 mm. to 10 mm. in length, giving the bur a total expanse of 3.9 

 cm. in length and about 2.8 mm. in width. 



Without question, it was this large-fruited form of Xanthium that 



1 Had Hooker seen plants of this species from other collections it is clear that he 

 would have cited them, since his citations of range appear in each case to be as 

 complete as his data at that time would permit. 



2 An examination of Hooker's text shows that a large proportion of the other 

 Douglas plants studied by Hooker had likewise come definitely from the banks of 

 the Columbia River. 



