BEHAVIOR OF SPECIES OF CACTI. 9 



a very noticeable feature of our work that even species native to 

 southern Texas make a smaller vegetative and a larger fruit produc- 

 tion when transferred to Chico; indeed, some species are decidedly 

 unsatisfactory in vegetative growth at the latter place. Some forms 

 from the Santa Rita Mountains of Arizona make less growth at Chico 

 than they do upon the deserts. During the past year plants of two 

 of them x made no vegetative growth, but they produced an exceed- 

 ingly heavy crop of fruit. 



EXCESSIVE DEVELOPMENT OF SPICULES. 



Just how environment acts to produce changes in plants or plant 

 structure is not possible to say. In the case of species of Opuntia, as 

 in those of other plants, all that can be done is to report the facts, 

 with little hope of explaining them. Attention has been called in 

 another place to the increased spine growth in keeping with gener- 

 ally increased vigor under cultivation. On the contrary, a dwarfing 

 of the plants by external unfavorable conditions often, but not always, 

 produces an increased development of spicules. Possibly the most 

 striking concrete example which has been studied is in the so-called 

 Indian-fig group of spineless forms. Practically all of these species, 

 when grown in close proximity to the coast in California, produce 

 more spicules than when grown in the more favorable atmosphere 

 of the interior valleys. Such hard conditions as those in the vicinity 

 of Indio, Cal., even when the plants are well irrigated, tend also to 

 decidedly increase the spicular growth. 



On the other hand, 20 miles from the Gulf coast at Brownsville 

 this group thrives well with no apparent increase in the production 

 of its armature. But such species as Opuntia gorcla are not at all 

 adapted and the spicules become much more prominent at Browns- 

 ville. 



In short, excessive development of spicules appears to be a direct 

 reaction from conditions unfavorable to vegetative growth. Such con- 

 ditions may be one or more of many. The dwarfing influence of the 

 seacoast is one; excessive heat, drought, alkalinity in the soils, and 

 possibly high winds may also be contributing factors. It is a matter 

 of common observation that in the same species plants stunted by 

 being robbed of their food and moisture by weeds and lack of tilth 

 bear proportionately more spicules than others in close proximity but 

 under more favorable conditions. This has been especially noticed 

 in low-growing species. 2 



1 Opuntia gilvesceus and 0. rufida. 



2 Opuntia leptocarpa and O. vulgaris. 

 9761°— 13 2 



