21 6 The Ohio Naturalist [\ol. 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 suminer 

 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 pennsylvanicum 

 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 nonnally under ordinary condi- 

 ditions. It will be found on examination that even for nonnal 

 burs, a certain percent have only one achene with an embryo 

 capable of development. 



