46 THE FRUIT OF OPUNTIA FULGIDA. 



tive material of the vegetative branch into one or tv70 fruits, instead of into 

 several scores, did not change the fate of the areoles on these fruits. There 

 was no increase of the vegetative activity in them such as might have been 

 expected as a result of the increased available food-supply. 



In seeking a reply to the second question proposed on page 45 it was 

 found that all attempts made by planting very young flower-buds to induce 

 these to become metamorj)hosed into vegetative shoots were unsuccessful. 

 The evidence from these experiments seemed to show that when once th& 

 growing-point of an areole has started, even if but barely started, to form a 

 flower, it can not be diverted and made to give rise to a vegetative shoot, as it 

 could by removing the fruit from the plant and planting it a few weeks 

 earlier. In every case the young flower-bud on a planted fruit either failed 

 to develop at all or developed but slightly and then withered. 



In essential agreement with these results in sprouting the detached fruits 

 are those observed in detached vegetative joints of Opuntia fulgida. Fallen 

 joints, as we have noted, very commonly take root and give rise to new plants. 

 In no case of scores observed were flowers developed from such rooted 

 joints until after a considerable shoot system had been formed. 



In Opuntia vulgaris, however, a series of experiments made in May and 

 June 1917, gave very different results. In practically every case the term- 

 inal joint or pair of joints removed just before the flower buds appear, or 

 just after they are visible, will root promptly and then develop normal flowers 

 and in most cases set fruit (see Hildebrandt, 1888, p. 110). 



The third question raised must apparently be answered by attributing to 

 the influence of polarity the restriction of flower buds to the most distal 

 areoles of the fruit. This is very pronounced so long as the fruit is attached, 

 and is definitely related to the base ; that is, to the point of attachment of the 

 fruit. In fallen fruits a much less definite polarity is exhibited which is 

 determined by the points of origin of roots and new shoots. 



Another problem suggesting itself in connection with the production of 

 flowers from fruits is the discovery of the reason for the fact that only the 

 terminal fruits of a cluster and a few of the subterminal ones give rise to 

 fruits, while all the fruits basal to these, from 1 to 8 or even 10, produce no 

 flowers. This seemed to be equally true whether this basal part of a chain 

 bore one or several secondary or branch chains upon it. In collaboration 

 with Dr. Hermann Spoehr, who planned the chemical side of the work, 

 analyses were made of the pulp of the two basal fruits and the two terminal 

 fruits of each of several chains of six or more fruits. We were unable, how- 

 ever, to discover any difference in the carbohydrates and other nutrient sub- 

 stances present in the distal flower-forming fruits and the basal sterile ones. 



