78 
Psyche 
[June 
Tourney has shown that certain species of cactus have almost 
lost the ability to produce seed but propagate by means of 
falling joints which take root, and yet their flowers are adapted 
to bees and are visited by a series of bees more or less peculiar 
to them. Thus Ashmeadiella cactorum Ckll. visits cactus at 
Santa Fe in July. 
These bees are usually short of flight. Some claim that this 
is so because they are small. Others want proof for such state- 
ments and offer other explanations. Thus Robertson (02) ex- 
plains it by saying that the short flight is the result of the visiting 
of the few closely allied genera of plants. In order to visit a 
few genera they have to be where those few are abundant. And 
so each year they nest in the neighborhood of the flowers on 
which they depend. Being near to these flowers each season, 
they are therefore short flighted. Both opinions are probably 
right. Apparently but little actual field work has been done on 
this problem. 
It is evident that there are other bees of this genus which 
are apparently limited by their environment as much as is 
Perdita opuntice. Thus M. H. Swenk and T. D. A. Cockerell (’07) 
Fig 4. — A drawing explaining Plate II, lower figure. This is a vertical section through the 
sandstone. The cells are shown as though the sand between them were transparent. In 
reality they are in several different planes. 
