THE PRTJIT OF OPUNTIA PTJLGIDA. 45 



The questions we liave to answer here are these : Why do areoles of fruits 

 that are picked and planted in April give rise, in the following month, to 

 nothing but vegetative shoots when if, on the other hand, these fruits were 

 to be left attached till May the same areoles would give rise in that month to 

 flowers, and to these only? Secondly, what sort of change occurs in the 

 areoles or fruit between April 1 and May 1 which makes the fruit detached 

 at the latter date incapable of doing what it could do if detached at the earlier 

 one ? Thirdly, why do none but the most distal buds of a fruit give rise to 

 flowers, while any but the most basal areoles of a fallen fruit may develop 

 shoots ? 



In regard to the first question, it has occurred to the writer that the 

 attached fruits give rise to flowers because these fruits and their areoles are 

 supplied with substances — perhaps flower-forming substances — ^which differ 

 markedly from those supplied to the areoles of the same fruit when it has 

 fallen and become rooted in the ground. Or, perhaps the process of root 

 formation may itself produce substances that inhibit flower formation in the 

 same fruit. The plan to experiment on this by rooting attached fruits in 

 pots of soil supported beneath them in the field has not yet been carried out. 

 Several attached vegetative joints of a plant growing in the greenhouse at 

 Baltimore, which from their position seemed likely to produce flowers, were 

 rooted in pots placed beneath them. In the first season, however, these joints 

 developed neither shoots nor fruits. It is planned to repeat this experiment 

 on attached fruits and joints in the field at the first opportunity. 



When a good-sized vegetative joint or two consecutive joints bearing sev- 

 eral fruits is rooted in the soil, these fruits still give rise to shoot-buds only. 

 This is true in spite of the fact that the conditions of nutrition here would be 

 expected to be more nearly like those of fruits on a growing plant. 



It was also attempted to discover by experiment whether the production of 

 flowers alone by attached fruits is definitely infiuenced by the amount and 

 kind of nutritive material available for them, in consequence of their rela- 

 tion to the vegetative branches bearing them and to other fruits. In each of 

 4 plants of Opuntia fulgida several branches were denuded of all fruits 

 except 3 or 4 sets of 1 or 2 fruits each. After three seasons' growth the num- 

 ber of new flowers and fruits that had arisen from these undisturbed fruits 

 was not at all abnormally increased, nor had the treatment induced the for- 

 mation of a vegetative joint on a single one of the original fruits. The chief 

 tendency of the new growth in these plants was toward the development of 

 new vegetative joints from the old, partially denuded ones. This was most 

 strikingly shown in a tree from which 300 fruits and 100 joints, including 

 the top of the stem, had been lopped off and only two fertile branches with 

 small fruit-clusters left. In this tree the new growth consisted almost 

 entirely of vegetative joints clustered about the cut ends of the main stem 

 and branches. In these cases, therefore, the diversion of all available nutri- 



