42 
CHARLES A. SHULL 
Kansas. This parent plant was given to Mr. Crevecoeur, who planted 
some of the burs in his flower garden in the spring of 1910. He secured 
a number of plants from them, and reports that "a portion of the 
plants bore the same kind of burs as the well known X. canadense, 
Fig. 2. Bur with wall removed to Fig. 3. Diagrammatic cross section 
show seeds. of a bur showing arrangement of seeds. 
while the major portion bore the same kind as the seed planted." 
This would seem to fix the relationship of the type to X. canadense, 
and Mr. Crevecoeur labelled the specimen in his herbarium X. cana- 
dense var. globuliforme. 
The following year, 191 1, seeds of the plants grown in 1910 were 
sent to Miss Grace Meeker, of Ottawa, Kas., who secured a third 
generation. All of the plants in this third generation were of the 
globuliforme type, but they produced burs which were small, and 
devoid of seeds. With these plants the group became extinct. 
Mr. Crevecoeur sent me quite a number of burs, and many seeds 
were planted, but all were non-viable. In some cases patches of cells 
in the cotyledons were still alive, but not a single hypocotyl showed 
signs of life. The early loss of viability in this case was partly due, 
no doubt, to the fact that the plants of the second generation, 1910, 
were destroyed while the burs were somewhat immature, in order to 
prevent possible escape from cultivation. It is quite natural that one 
sholud not desire the survival of a cocklebur producing twenty or more 
seeds to the bur! 
In the spring of 1915 two of the burs still remaining from the original 
parent were planted at Onaga, but the seeds did not germinate. The 
possibility of studying the inheritance of the bur characters in crosses 
