61 



show most pronounced spines. An experiment which might 

 throw a great deal of Hght upon the influence of drought condi- 

 tions upon the sterihty of the fruit in this species ought to be 

 undertaken. Cuttings from a plant which in nature is nearly 

 sterile should be grown under artificial irrigation. With suitable 

 checks the influence of drought upon sterile conditions might be 

 shown. The influence of this factor in the lack of seed-produc- 

 tion in cultivated and other crops of course is well known but we 

 have here an entirely different condition of things. This is not a 

 case of temporary lack of seed-production caused by temporarily 

 abnormal conditions but apparently at least habitual sterility 

 brought about in a given perennial species growing in a certain 

 situation and not taking place in the same species in another 

 situation but a few miles removed, and this sterility accompanied 

 by a simulation on the part of the fruit of one or more of the 

 caulome characteristics. My observations indicate that it is on 

 the desert mesas that the largest proportion of the sterile-fruited 

 forms occurs in this species and that fruits of those plants growing 

 in the foothills are more likely to be spineless. 



There is probably no species of Opuntia in which the fruit 

 simulates the stem more closely than in 0. subidata. In planta- 

 tions which have been examined in this country fruits with no 

 constriction between them and the stem were the rule rather than 

 the exception. In other words, the fruit in a very large per- 

 centage of cases was imbedded in the end of a branch.* Pro- 

 liferous ones are also very common. Such features are equally 

 true of 0. cylmdrica and the imbedding of the fruit in the end of 

 a branch is not at all rare in 0. spinosior, 0. versicolor and 0. 

 arborescens. It is apparently more common in these species 

 under cultivation. 



The union of fruit and joint or the imbedding of the fruit in a 

 joint is very common in the Platyopuntias and apparently it is 

 more abundant in some species than in others. In a spineless 

 form of 0. cldorotica of which we have seen no mention in litera- 

 ture, the phenomenon is so common in some localities in southern 



* See also Schumann's Gesamtbeschreibung d. Kakt. 68i. /. /oj. 1899. 



