THE FRUIT OF OPUNTIA FULGIDA. 7 



Certain of the peculiarities above noted in the fruits and seeds of Opwntia 

 are, it is true, found in a few other plants, though in none of which the 

 writer has found record is there such an aggregate of unusual features of 

 development, and certain of these features are unknown outside the genus 

 Opuntia. 



The persistent attachment and continued gro^\i;h of the fruit just noted is, 

 as far as I can learn, recorded for but one other family of angiosperms, the 

 Mvrtacese. In the genera Callistemon and Melaleuca, for example, the 

 fruits may persist for 10 or 15 years. In the former, according to Ewart 

 (1907), the fruit opens and discharges the living seeds only when it has been 

 killed by the cutting off of its water-supply. This latter may happen in 

 consequence of severe drought, of the breaking off of the branch bearing it, 

 or from the death of the branch or whole tree from fire or other cause. 



There, are, however, three important differences between the behavior of 

 the fruits of this Australian "' bottle-brush " tree and those of such opuntias 

 as the " choUa " (0. fulgida). In the first place, the persistent fruit of 

 Callistemon does not possess axillary buds and therefore does not, like 

 Opuntia, give rise to secondary and tertiary flowers and fruits from these. 

 Secondly, the fruits of the bottle-brush tree, though they may open and dis- 

 charge their seeds with the first cutting off of the water-supply, do not them- 

 selves fall from the tree until some time after they are dead ; hence, they can 

 play no part in the vegetative propagation of the species. Thirdly, the 

 seeds of Callistemon are ultimately shed from the fruit to play the most 

 important role in the dissemination of the plant, while the seeds of the fleshy 

 fruits of Opuntia fulgida are, as we have seen, never discharged and appar- 

 ently rarely germinate under natural conditions. 



From this comparison of the opuntias with the only other family of plants 

 having fruits with similar jjeculiarities, it is clear that these Cactacese have 

 become much more abnormal as regards the behavior of propagative struc- 

 tures than any other family of angiosperms. Moreover, the readiness with 

 which a growing-point destined to give rise to a flower may be induced to 

 form a vegetative shoot (by the mere separation of the fruit bearing it from 

 the parent plant) suggests the possibility of discovering here some of the 

 causes detennining the production from the same meristematic mass, in one 

 case of a reproductive organ or in another of a vegetative shoot. 



With this much of suggestion of the structures and phenomena we are to 

 deal with, we shall now examine more closely into the development and fate 

 of the flower, fruit, and seed of certain opuntias. We shall be concerned 

 primarily with those of Opuntia fulgida, in which these structures have been 

 studied most carefully in Tucson, Carmel, and Baltimore. Incidentally we 

 shall also note the structure and capacity for propagation of the vegetative 

 joints of certain species, in order that we may compare with them the 

 structures and phenomena observed in sprouting fruits. 



