4 BULLETIN 31, U. S. DEPARTMENT OF AGRICULTURE. 



on one side of the plant and spineless on the other, the contrast pro- 

 ducing a very striking appearance. 



This habit of reversion or bud variation, whichever it may be con- 

 sidered, is a very important characteristic, and, while more striking 

 m the above variety than any other which has been cultivated in 

 these investigations, appears to be not at all uncommon. A plant of 

 another spineless variety on hand now bears promise to be just as 

 conspicuous a few years hence as this one. It started to vary in the 

 same direction last year. 



All this relates, however, to the development of characters economi- 

 cally undesirable. It is well known that lack of spines is also a char- 

 acter which can be maintained by vegetative propagation, but being 

 usually of slight variation is not as striking as the case mentioned of 

 variation in an opposite direction. This phenomenon is an import- 

 ant one, for it furnishes a possible suggestion regarding the origin of 

 the spineless varieties. 



Both of these variations appear to the writer to point to the origin 

 of the spineless species of the so-called ficus-indica group from the 

 spiny ones, the spineless forms being the result of a long series of 

 selection, both upon this continent and in the Mediterranean region, 

 subsequent to their introduction there. The striking variation of 

 certain spineless forms to a spiny condition is looked upon as a re- 

 version to an original type. 



In both of the striking examples of reversion referred to, the 

 development of spines is associated with a bilateralism in the joint. 

 In both cases one or two pulvini on one side of a spineless joint 

 developed several large spines. A new joint on the same side and 

 from a neighboring pulvinus was totally spiny. While this example 

 of reversion and the common cases of variation to a less spiny condi- 

 tion in this group are marked and can be reproduced vegetatively, 

 many species handled during the past six or seven years, consid- 

 ered to be very promising agriculturally if their spines were elimi- 

 nated, have not proved sufficiently variable in spine characters to 

 warrant any great promise in handling them. Doubtless the best 

 species for southern Texas conditions is Opuntia lindheimeri and 

 related and associated species, but 0. lindheimeri is not a variable 

 species. In all the seedlings grown and the vegetative propagations 

 made in the past several years no individual plants have been seen 

 which showed any tendency toward spinelessness. On the other 

 hand, there are other species (Pis. II, fig. 2, and III, fig. 1) in 

 southern Texas which are variable, and some forms of them are 

 nearly, if not quite, spineless, although they always have spicules 

 to a greater or less degree. All of these native variable varieties 

 known to us are rather slow of growth as compared with the more 

 spiny species. Being hardy to 10° F., or possibly, in rare cases, to 



