THE FRUIT OF OPTJNTIA FULGIDA. 51 



Taking into account all four of the peculiarities mentioned, it is clear that 

 Opuntia fulgida is, on the whole, the most generally peculiar type studied, 

 followed most closely perhaps by 0. arbuscula and 0. catacantha. At the 

 other end of the graded series is Opuntia versicolor, which behaves like a 

 normal angiosperm in most, or perhaps all, cases where it is not stimulated 

 by the cactus fly, Asphondylia. 



It is evident (from observations made in Arizona, in the cactus garden 

 of the Bureau of Plant Industry established by Doctor Griffiths at Chico, 

 and from records in the literature, of cases such as Opuntia prolifera, 

 0. cholla, 0. spinodor, etc.) that many other species of Opuntia fit in at 

 various points in the series described above. In other words, in the genus 

 Opuntia the ovary, in flower and in fruit, may assume now more, now fewer 

 of the various functions of the vegetative joint. Of the Opuntia fruits thus 

 far studied from this point of view, that of Opuntia fulgida seems not only 

 the most atypical angiospermous fruit among these Cactacete, but is perhaps 

 also the most aberrant (shoot-like) fruit to be found in all angiosperms. 



PROLIFERATION OF JOINTS AND FRUITS IN 

 RELATION TO THE STERILITY OF FRUITS. 



From what has been said above of Opuntia fulgida it is evident that the 

 propagation of this cactus has ceased to depend chiefly on the development of 

 fertile seeds, and so of seedlings, but is accomplished more largely by the 

 vegetative sprouting of fallen joints and of fallen fruits. The propagation 

 of the species by the rooting of joints or parts of joints is rather common in 

 several genera of Cactacese, such as Cereus, Mammillaria (Goebel, 1889), 

 Peireskia, etc., in addition to many and probably most species of Opuntia. 

 The propagation by means of the fallen fruit is probably common among 

 opuntias with persistent fruits. Besides its occurrence in the forms already 

 mentioned, it is apparently common also in 0. prolifera, 0. cholla, 0. 

 spinosior, etc. 



In a number of other opuntias and certain other genera there are devel- 

 oped, in addition to the true fruits and ordinary vegetative joints, more 

 specialized short joints which are often bead-hke or more or less fruit-like in 

 character. These occur, for example, in 0. arhuscula, 0. catacantha, 

 0. fulgida, 0. leptocaulis, 0. tetracantha (Toumey, 1905), Mammillaria 

 gracilis (Goebel, 1889), a species of Cereus, etc. In each case these struc- 

 tures are capable, after falling, of taking root in the soil and thus starting 

 new plants. 



Taking this whole series of structures, together with the various sorts of 

 joint fiTiits that occur in 0. fulgida and many other opuntias, and the many 

 seedless opuntia fruits, it might be assumed that the fruit of these Cactacese, 

 and especially of the opuntias, is losing its primary function of seed-produc- 

 tion. It is evident at least that the production of new plantlets and the 

 function of dissemination has been taken over in large part by these various 



