216 
The Ohio Naturalist. 
[Vol. XIV, No. 2 , 
THE SPROUTING OF THE TWO SEEDS OF A COCKLEBUR. 
John H. Schaffner. 
In 1901, Masterman reported some observations on the sprout¬ 
ing of cocklebur seeds, showing that both seeds of a bur usually 
sprout in the same year. This conclusion was at variance with 
Arthur’s experiments; for Arthur had reported that the germina¬ 
tion of both seeds of a bur of Xanthium in one season was excep¬ 
tional. Crocker, in 1906, in his paper on the role of seed coats in 
delayed germination, reported tests on various cockleburs and 
stated that high temperature had a decided effect on the sprouting 
of the seed of the “upper” achene. This fact, no doubt explains 
most of the discrepancies of reported observations and experi¬ 
ments. 
In 1909, the writer studied sprouting cockleburs on the sandy 
upper beech at Cedar Point, Ohio. A great majority of the burs 
buried in the sand were sprouting both embyros. In the summer 
of 1913, further observations were made. Because of the dry 
weather very few seeds of any kind were sprouting on the upper 
beech but on the bay side of the Point various low, moist, sandy 
areas contained abundant cocklebur seedlings. The plants all 
seemed to belong to the species, Xanthium pennsvlvanicum 
Wallr. Most of the burs had two seedlings. Of those juvenile 
plants, one was usually larger than the other, as might be expected. 
Of course, it was not possible to determine whether these burs 
were one or two years old. But there is no question that in sandy 
soil with abundant heat and exposure to the sun, the two embryos 
sprout in the same season. And this is the practical side of the 
question for the fanner. In a cold climate under certain soil 
conditions only one embryo may sprout the first season and the 
other one the second, or even later. 
In most cases the one seedling is considerably larger than the 
other as noted above. This would be expected if one begins to 
sprout earlier than the other. But there is frequently a difference 
in size and perfection of the two achenes in the bur. This dif¬ 
ference is probably often simply caused by abortive development. 
The cocklebur has evolved from a small flower cluster, only two 
flowers remaining. There is little room in the bur and so in the 
struggle for space and food one achene often has the advantage 
and develops a better seed than the other. Probably in some 
species, the one seed is becoming vestigial while in others both 
achenes still have room to develop normally under ordinary condi- 
ditions. It will be found on examination that even for normal 
burs, a certain percent have only one achene with an embryo 
capable of development. 
