106 CARNEGIE INSTITUTION OF WASHINGTON. 



The development of vegetative shoots from an attached fruit is as 

 rare in Opuntia fulgida as in 0. versicolor, only two cases having been 

 seen in hundreds of plants examined. In Opuntia arhuscula, however, 

 the lower of the attached fruits of certain plants regularly give rise to 

 condensed vegetative shoots of several internodes each. When these 

 fruits are put on damp soil the condensed shoots push out to initiate 

 new plants. Attempts to artificially produce this vegetative prolifer- 

 ation of the areolae of attached fruits of Opuntia fulgida, by removing all 

 but three of the fruits of a cluster of 150, failed. In all the experimental 

 plants thus far examined the few fruits left gave rise to flowers only, 

 just as the fruits of the undisturbed clusters do. 



The flowers of Carnegiea gigantea show certain irregularities in dis- 

 tribution and rate of development. These irregularities were studied 

 by the aid of a compass in scores of crowns in the field and were accu- 

 rately plotted for a number of typical crowns taken into the laboratory. 

 The flowers were found to be either far more numerous on the east 

 side of the stem, or, if more equally distributed, the flowers of the east 

 side are more advanced in development. This one-sided growth is, 

 perhaps, dependent on the liigher average temperature of the east side 

 of the thick stem, due to the fact that this side is not only first warmed 

 by the sun in the morning, but also retains its temperature till late in 

 the afternoon because of the relatively high temperature of the air from 

 mid-day till sundown. 



