THE AMERICAN BOTANIST 



57 



1 



While various degrees of size 

 occur, two embryos, one decidedly 

 smaller than the other, but vigorous 

 and slightly connected at the base 

 ( fig. 1 ) , are by far the most common. 

 Three embryos from a single seed 

 have been found but once, although 

 they are not uncommon in 0. vul- 

 garis. The embryos are but slightly 

 connected and are easily separable 

 and a few are not connected at all, or 

 if so, become separated in the earliest 

 stages of germination. Occasionally 

 an extremely minute embryo is found 

 which in germination is never seen 



connected with the larger plant, but escapes from the testa when 

 the latter is just appearing (figs. 3 and 4). In these minute 

 embryos, roots are never developed and the plants die within a 

 few days. Rarely specimens with three cotyledons are found 

 but otherwise the plants appear so normal as to make it seem 

 doubtful that there are two embryos closely united, but rather 

 that these are single plants with three cotyledons, (fig. 2). 



In Opiintia vulgaris^ it was found that usually but one 

 .embryo developed and hence that polyembryony could be of 

 little service to the species, but in O. Rafinesqtiii among em- 

 bryos started in the early spring of 1914, all except the minute 

 ones were still alive and flourishing in June 1915. 



This is the third case of polyembryony noted among the 

 Cactaceae, the others being in O. vulgaris and O. tortispina. The 

 latter is figured by George Engelmann in his ''Cactaceae of 

 Whipple's Expedition", showing two embryos both fairly large 

 and slightly connected, the usual situation in O. Rafi]icsquii. 



