Books and Current Literrature. 



93 



them, so that this feature can be left out of consideration from 

 an economic point of view, though it involves principles of great 

 scientific interest. 



It is essential to remember that these plants cannot be put 

 out to shift for themselves; they must be farmed like any other 

 crop, though, owing to their resistance, they permit more latitude 

 in their treatment than most other plants. The map, Fig. 5, 

 shows in a graphic way where spineless cacti, according to present 

 knowledge, are adapted to grow. There is no doubt, however, 

 that in time they may be bred to withstand a greater degree of 

 cold, thus extending somewhat the area within which they may 

 profitably be grown. The prickly pear plants, as they now 

 exist, are adapted to a region having considerable rainfall, but 

 too irregularly distributed for ordinary crops. They must 

 have water to grow and considerable of it. They are the camels 

 of the vegetable world. They must have water, but they can 

 get along for long periods without it. What is most needed in 

 the spineless prickly pears today is greater hardiness, but this 

 quality cannot be bred into them in two or three years. It might 

 be possible, by careful breeding and selection, in a decade or 

 more to increase the hardiness of the rapid-growing prickly pears 

 so as to withstand a temperature of somewhere about zero, 

 instead of 20° or 25° F., which are the limiting temperatures 

 now, and this would push the limit of their cultivation to the 

 northward very materially. But this will take much patient 

 toil and many years of experimentation. 



There are two ways of attacking the problem. One may 

 depend upon selection alone. To gain hardiness by this method 

 one would be obliged to discard the present spineless specie? 

 entirely and work with the hardy spiny natives, for it cannot be 

 expected that the spineless forms can be so improved within 

 themselves as to withstand 25 degrees more of cold than they 

 do now. The other way is to hybridize the present spineless 

 forms with some hardy plant possessing as many desirable 

 characters as possible. It will usually be necessary to grow this 

 hybrid to maturity, plant its seeds, and then begin a long series 

 of selections from these so-called second generation hybrids. 

 Hut it will take a season to produce the hybrid, five years more 



