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CIRCULAR 66, U. S. DEPARTMENT OF AGRICULTURE 



A study of vegetative reproduction in such forms as Opuntia 

 luiffuiforrms (pi. 18, A) would be exceedingly interesting. Certain 

 strains of this species at least produce plants simulating the type 

 of joint from which they are propagated. As an example, the plant 

 illustrated in Plate 18. B, will reproduce itself vegetatively from the 

 median strap-shaped joints, the lateral ovate ones producing a plant 

 of entirely different appearance in that none of the long joints will 

 be formed. 



A study of the plants in the wild reveals some remarkable behavior 

 in certain individuals. One prickly pear closely resembling Opuntia 

 bentoni is recalled. It was found near San Antonio, Tex. The 

 fruits habitually turned red in late summer like most species, but 

 did not drop off as usual. Instead they turned green again during 

 the winter and became incorporated as a permanent part of the 

 plant, becoming vegetative, and giving rise to vegetative growth the 

 next season. This growth was propagated for four or five years at 

 Chico, Calif. The seed of these vegetatively turned fruits at 3 



years of age showed 

 unmistakable signs 

 of erosion, indicat- 

 ing that an absorp- 

 tion by the plant 

 of the once presum- 

 ably fertile, sexu- 

 ally produced seed 

 was taking place. 

 The behavior of 

 seed in fruits which 

 have given rise to 

 plants by vegeta- 

 tive means has received scant attention, but would make an interest- 

 ing piece of investigation. 



A scientific study of fasciation (pi. 14, A) in these plants has 

 received practically no attention. Since these aberrant forms are 

 so much sought after by fanciers, investigations for the purpose of 

 finding how to produce them might yield some economic results. 



It would be very interesting to know just what takes place when 

 the fly {Asphondylia opuntiae) deposits its eggs in opuntia fruits. 

 By what adaptation do these fruits remain attached to the plants 

 until May or June of the second year after the insect has emerged ? 

 In this case the fly causes the fruit to produce vegetative joints, 

 but an aphis on another species causes fruits to proliferate into other 

 fruits. (PL 18, B.) 



The origin and significance of the various structures in the pulvini 

 or cushions (fig. 1) have never been worked out. Indeed, their 

 morphological significance is not known. Some of them are not even 

 named and have not received attention in systematic works. 



A comparative study of spineless forms and the species from which 

 they are derived would be profitable. Much light could be thrown on 

 the subject by growing seedlings of the spineless forms. 



An exhaustive study of the fruits of certain species which com- 

 monly are sunken into the body of the plant and their future be- 



Figure 2. — Tip of a small spine of Opuntia confusa, highly 

 magnified, showing the retrorse barbs, a characteristic of 

 the genus Opuntia. X 350 



