56 



small fraction of the differentiation which had been achieved 

 in pre-scientific days, much of it, as with the cabbage group, 

 in pre-historic times. 



How did these old varieties come into existence? What can 

 we guess as to the probable basis for their original selection and 

 preservation? In the case of the cabbage group, it seems rea- 

 sonable to suppose that some primitive food-gatherer, out 

 collecting the daily supply of vitamines for her family, chanced 

 upon a plant of this wild mustard type which made better 

 "greens" than the common run of the species. Presumably 

 such a better type must have been noted sometime, and pre- 

 served for later artificial propagation. 



What caused the new type? The same cause that has under- 

 lain the production and discovery of most kinds of cultivated 

 things, — chance variation, or as it is also called, spontaneous 

 mutation. There could hardly have been any purposive hybrid- 

 izing back of it, for it is only relatively recently that hybridiz- 

 ing has entered into the common practice of plant breed- 

 ers in general. Most new varieties have arisen by unexpected 

 and unpredicted variation, just as in the case of the commer- 

 cial Boston Fern, from which hundreds of distinct new forms 

 have appeared during the last thirty-five years. 



With regard to the cactus, spineless types of which have 

 received a great amount of newspaper publicity during the 

 past twenty-five years, it seems to be true also that the best 

 varieties are old, antedating any definite records of their 

 producer. Professor Thornber, of the University of Arizona, 

 some years ago, made a careful experimental cultural test of 

 as many different kinds of spineless cacti as could be obtained, 

 and found that the best and most vigorous grower in his sec- 

 tion of Arizona was not any recently advertised commercial 

 variety, but a Mexican Indian type which had been cultivated 

 since before Columbus, at least. 



Again contrary to general belief, he found that for cattle 

 forage purposes, the spineless varieties which had strongly 

 been promoted as holding great promise for the extension of 

 cattle raising in the dry Southwest, were practically useless. 

 The reason for this is simple. It was found that even the old 

 Indian variety could not be grown on the open range, because 

 the cattle would browse it so close as to kill it, if they got the 



