38 THE FRUIT OF OPUNTIA FULGIDA. 



PROLIFERATION OF FALLEN FRUITS. 



If the fruit of Opuntia fulgida remains attaclied to the tree the only struc- 

 tures produced bj its areoles are trichomes, nectaries, and flowers. This is 

 practically universally true. Among many hundreds examined, only two 

 cases were seen in which a vegetative shoot had arisen from an attached 

 fruit. If, however, fruits are plucked from the tree and placed on moist 

 soil, there arise from their areoles not flowers but roots and later vegetative 

 shoots, and so new plants are initiated ; that is, if any given fruit remains 

 attached there may arise from the growing-point of a certain areole a rela- 

 tively short shoot which develops leaves and axillary buds, but soon ends its 

 activity with the formation of a set of stamens and carpels. If the same 

 fruit were detached the same areole, and thus the very same gTowing-point, 

 may give rise to a shoot of unlimited growth, while other areoles near the 

 soil form adventitious roots. This production of new plants from buds on 

 the wall of the ovary in the fruit is a surprising phenomenon ; in fact, it is as 

 unique as the formation of flowers from axillary buds of the ovary of 

 the unopened flowers. 



This process of the vegetative sprouting of a fruit planted in soil to a new 

 plant often occurs in 50 to 75 per cent of fruits planted in the greenhouse. 

 In the field about Tucson, at least in the spring of the year, it occurs but 

 rarely. A careful examination of some scores of young plants of this 

 species, of 3 or 4 joints in height, in the desert near Tucson, in May 1915, 

 showed that all had arisen from fallen vegetative joints. None of the fallen 

 fruits seen at this time showed any preparation for the development of new 

 plantlets. This is the more surprising because the soil had been considerably 

 moistened that season by unusually copious rains. In September, however, 

 a careful search by an assistant, B. R. Bovee, revealed a few very young 

 plants which had evidently arisen from fallen fruits. It is possible, there- 

 fore, that under some conditions, such as those existing during years of 

 favorable summer rains, a considerable number of new plants may thus arise 

 from fruits. 



The origin of new plants from rooted fruits will be described as it has been 

 observed in the greenhouse. The process is clearly the same in the field, as 

 far as could be seen from the few plantlets found there. Many different 

 plantings of the fruits were made at Tucson in April and May, at South 

 Harpswell in July and August, and at Baltimore in February, October, and 

 December. These all gave substantially the same results, in spite of the fact 

 that the Tucson plantings were of fruits that would in a week or two have 

 produced flowers if they had been left on the parent plant, while those 

 planted in Baltimore had entered into the resting-stage for the winter (figs. 

 78,99). 



Fruits that are half-buried in a soil that is kept moist but not saturated 

 may begin to form adventitious roots within the first week. In 5 weeks' time 

 the finiit has been found fastened securely in the soil by several roots, some 



