BEHAVIOR OP SPECIES OP CACTI. 17 



after a low temperature is remarkable in many species. Limbs 

 which have become discolored and droop through an angle of 90° 

 or more will often recover and regain their normal position. This 

 has been strikingly illustrated in several instances in connection with 

 spineless forms. In one case, where a loss of at least 50 per cent was 

 estimated from a heavy freeze at Chico, the result was an actual loss 

 of not over 2 per cent. Under no consideration should the plants 

 be cut, bruised, or handled at such a time, for the results are always 

 disastrous on account of the rapid rotting which is thus promoted. 



Plate V and Plate VI, figure 1, give a graphic representation 

 of the effect of low temperatures upon " cardenche " 1 at San An- 

 tonio. This is a cylindrical species and consequently more sus- 

 ceptible of graphic representation than the flat- jointed forms. 

 Plate VIII shows the same plant before and after recovery from 

 the effect of a spell of cold weather. It will be noticed that in one 

 view the branches hang limp by the side of the stem; in the other 

 they have recovered almost to their normal position. In some cases, 

 as represented in Plate VI, figure 1, the recovery is not complete and 

 the limbs hang down permanently, but are not injured further than 

 this. This species grows spontaneously upon the highland of Mexico 

 and is at about its limit of hardiness at San Antonio, where the 

 photographs for Plate V and Plate VI, figure 1, were taken. In no 

 case has any visible permanent injury been done, resulting in an 

 actual loss of portions of the plant during the period of experi- 

 mentation, although the condition seen here has been common. The 

 condition shown in Plate V, figure 2, was brought about by a tem- 

 perature of 18° F. in February, 1905. In the following April the 

 plant had recovered, as shown in Plate V, figure 1, left-hand plant. 

 The same phenomenon occurs, but in a less conspicuous way, in the 

 flat- jointed forms. 



As stated above, the effect of low temperatures is precisely the same 

 on the spineless economic species, but they are less strongly con- 

 structed at the articulation between joints. The drooping is conse- 

 quently more easily brought about, more pronounced, and more likely 

 to result in the breaking off of large limbs. At San Antonio the 

 spineless forms have gone down in a heap of disorganized tissue from 

 which there is no hope of recovery. At Chico, on the contrary, the 

 drooping, weakened condition of the nodes has occurred several times, 

 but the recovery has been all but complete. 



In the Salt River Valley of Arizona one of the hardest of the 

 spineless forms is grown. Here it is a matter of common observation 

 that the low temperatures of winter often trim the plants severely 

 by the same process as that mentioned above. 



1 Opuntia imbricata. 



