60 



An examination was next made of fruits from the same plants 

 giving rise to branches but not to fruits. They showed fertile 

 seed as follows : o, o, 3, 4, 4, 4, o, 5, 6, 8, i, 3. 



Again another examination of normal fruits bearing neither 

 fruits nor branches was made, with the following results : 4, 8, 

 o, 9, 9, 4, 10, 6, o, 4, 6, 10, 8, 3, 5. 



The above figures are very suggestive but nothing more than 

 that. At least a hundred times more data are necessary to en- 

 able one to draw conclusions. But they represent all the data 

 that limited time could secure. The tunas which had been de- 

 pended upon for food and water for about ten hours failed to sat- 

 isfy longer, necessitating a postponement of the investigation. 



To summarize we might tabulate as follows : 



1. The proliferous form of the plant is sterile, so far as I have 

 been able to determine, absolutely. 



2. Fertile seed in fruits giving rise to other fruits average 1.7. 



3. Fertile seed in fruits giving rise to vegetative branches 

 average t,.6. 



4. Fertile seed in non-proliferous fruit average 5.7. 



Similar observations might be made upon O. Icptocau/is, a 

 closely related plant of very similar habit. 



The simulating of the stem by the fruit as it loses its fertility 

 is very evident in Opuntia fulgida. Normally, the fruit of this 

 species is spineless or, at most, bears only a few fugacious, hair- 

 like, unsheathed spines in the normal fertile specimens. In many 

 cases, however, certain plants will be found in which the fruit 

 bears a goodly proportion of sheathed spines like those of the 

 stem. Experience shows that these spiny-fruited forms bear 

 much fewer fertile seeds than those which do not bear spines. 

 It is equally apparent that it is in the drier situations that sterility 

 occurs and that spines develop on the fruits when they are two 

 to four or five years old, while there may be no evidence of them 

 the first year. For the benefit of those not familiar with 0. ful- 

 gida, it should be stated that the fruit is proliferous, one develop- 

 ing from another until there is a branched, pendant bunch, in 

 some cases a foot long, remaining attached to the plant for a 

 number of years. It is the proximal ones of the bunch which 



