42 THE FKiriT OF OPUNTIA FULGIDA. 



observed in certain other Arizona opuntias. The most striking case of those 

 studied is afforded by Opuntia versicolor, a species in which the normal 

 structure of shoot, flower, and fruit is quite similar to that found in Opuntia 

 fulgida. 



The fruit of 0. versicolor is quite variable in form, size, and habit as to 

 ripening and persistence. It may be nearly globular and from 15 to 20 mm. 

 in diameter, as is true of most of the smaller fruits, or it may be a much-elon- 

 gated structure whose whole length is 4 or 5 times its diameter (figs. 82, 84). 

 These fruits do not soften greatly or change color with the ripening of the 

 seeds, but remain green or yellowish during the autumn and, according to 

 Toumey (1898), usually ripen, wither, and dry up while still on the tree 

 during early winter. Some of the apparently normal fruits, however, as 

 Toumey noted, may remain attached for a year or even two years. This is 

 demonstrated by figures 82, 83, and 86, which were photographed in late 

 April. 



On examination of large numbers of these plants of Opuntia versicolor in 

 April and May, it was found that most of them (about 75 per cent) bore no 

 persistent fruits. Of those plants which did bear apparently normal per- 

 sistent fruits, 9 out of 10 bore abnormal gall-like fruits also, of which we 

 shall say more presently. It seems possible then, that the cause of the per- 

 sistence of the normal fruits may be the same as the cause of the abnormality 

 as well as of the persistence of the far more common gall fruits. 



These gall fruits have an exceedingly interesting developmental history. 

 They seem very clearly to be caused by the deposit in the flower-buds of the 

 eggs of the cactus fly (AspJiondylia opuntice). These eggs may apparently 

 be deposited at different times in different cases, for the galls show that the 

 flower bud has been arrested and diverted from its normal course at different 

 phases of its development. The galls show that in some cases the arrest of 

 normal development of the flower occurred when the perianth had hardly 

 been initiated, in other cases after the perianth had been half-formed, and 

 in. yet others not until the perianth was fully developed (fig. 84, a, h, c, d). 



The degree of disturbance of the normal development of the internal 

 organs of the flower differs markedly. In some cases the stamens, pistils, 

 and even the ovules may have been well started only to become distorted and 

 withered without maturing, while in others no traces of stamens or ovules 

 are to be discovered. Quite independent of these internal features are the 

 size and external form attained by the distorted bud. Sometimes it may be 

 no larger than some normal buds at the time of opening, while again it may 

 reach a length and diameter twice or thrice the normal (fig. 84 a, c). In 

 general external appearance most of these fruits in early April have a plump 

 green ovary and often dark-red, waxy petals. Many of them, in fact, look 

 precisely like gigantic, but otherwise normal flower buds that seem just 

 ready to burst into bloom (fig. 84d). It is surprising that the petals can 

 persist all winter and retain a color which though darker than the outside of 



