BEHAVIOR OF SPECIES OP CACTI. 23 



deed, some of the desert species seem to require more water in starting 

 from cuttings than do the spineless ones, although when established 

 they thrive on much less water. This is to be interpreted to mean 

 that the desert species root much less readily and consequently are 

 more withered before they become established than the spineless ones. 

 As the season advances here, there is less and less moisture in the soil, 

 giving the forms which root quickly a decided advantage over the 

 others. 



SUMMARY. 



(1) Spiny plants grown near the coast of Texas mature their 

 spines much more slowly than in drier regions. This makes them 

 more difficult to singe. 



(2) A variation in the number of spines is characteristic of certain 

 species. In other species there is practically no variation. 



(3) Many of the hardy species of southern Texas are not promis- 

 ing for breeding by selection, because of a lack of variation. They 

 are very constantly spiny, and spine production is directly propor- 

 tional to general plant vigor. 



(4) The indications, so far as they exist, are that the spineless 

 species have been derived from spiny forms. 



(5) Conditions of growth may decidedly modify the spination 

 and especially delay maturity of some species. 



(6) In general these plants adapt themselves well to changed con- 

 ditions. The spineless forms, many of the Mexican highland species, 

 and the genus Nopalea in general thrive well with an abundant 

 moisture supply, but the species from the drier regions are difficult 

 to grow where the supply is constant and are much more difficult 

 to establish under any condition. 



(7) All forms thrive best when the moisture supply is low during 

 the dormant season. 



(8) Wherever tried, some species or form native to the region has 

 proved more productive than introduced forms. 



(9) Environmental conditions appear to have more effect on the 

 production of spicules than on the production of spines. In gen- 

 eral, factors which are unfavorable to vegetative production appear 

 to stimulate the growth of spicules. 



(10) The conditions in southern Texas appear to be decidedly 

 favorable for the production of vegetative growth, while those in 

 California are better adapted to fruit production in these plants. 



(11) Prolonging the growing season by housing appears to in- 

 crease vegetative growth at the expense of fruit production. 



(12) A few species behave peculiarly at San Antonio. Their 

 period of life appears to be very much shorter than at either of the 

 other localities. 



