10 BULLETIN 31, U. S. DEPAETMENT OF AGEICULTUEE. 



LOCALITY VARIATIONS. 



A careful comparison of a large number of species in the different 

 localities in which the experiments of the Bureau of Plant Industry 

 have been conducted would be exceedingly interesting and instruc- 

 tive. However, only the salient features can be touched upon here. 

 One or two striking cases of behavior are detailed and an attempt 

 made to state the generalities of groups rather than the behavior of 

 individuals. But it must be remembered that groupings in such 

 genera as Opuntia must revolve about certain species more or less 

 closely related until a more definite, logical classification has been 

 adopted. 



The three main localities in which these species of Opuntia have 

 been grown during the past six years differ very widely in their 

 meteorological and soil conditions. The behavior of these plants, 

 which as a group are adapted to live and thrive for long periods 

 without rain, has in many cases been very striking. The plants be- 

 have in certain roughly defined groups, not always but sometimes in 

 groups of such natural affinities as would be considered by the bota- 

 nist, but more often in what might be called geographical groups. 

 These are in some instances more or less natural as well. 



At Chico, Cal., the " tapona " group 1 of Mexican highland species 

 under cultivation behave vegetatively in quite a normal way, al- 

 though one species, as discussed elsewhere, is very abnormal in its 

 fruiting habits. Here the seasonal rainfall is propitious although 

 reversed, the moisture occurring in the winter instead of in the sum- 

 mer growing season. On the whole, however, the conditions are 

 quite comparable when the element of cultivation is introduced to 

 prolong the season of available moisture into the otherwise longer 

 dry summer. The plants are more tender, owing to the super- 

 abundance of winter moisture when they normally should be dry 

 and. to the rather low temperatures of the region. The plants, how- 

 ever, are no more gorged with water in the spring at Chico than 

 they often are in the summer in their natural heath. This applies 

 to other groups as well. In point of size and color they do not differ 

 materially from their original form except that Under the stimulus 

 of clean cultivation they grow more rapidly. 



At Brownsville, Tex., this group is perfectly hardy, very poor in 

 fruit production, and abnormally large of joint. It is common for 

 some of the spiny forms to have joints 18 inches to 2 feet in diameter 

 at 2 years of age. The number of joints produced is no more than 

 normal. Among the spineless members of the group the joints 

 produced at Brownsville, of course, are smaller, but much larger than 

 is normal for the same varieties in Mexico. The thickness of the 



' Opuntia robusta and its allies. 



