440 



THE AMERICAN NATURALIST 



[Vol. L 



We have supplemental evidence that the cacti grow most suc- 

 cessfully in such warm temperate moderately arid regions as have 

 precipitation in the warm season from the work of the Australian 

 commission for the study of certain species which have escaped 

 from cultivation in several countries, especially Australia, and 

 have become a pest. 5 In Queensland and New South Wales 

 species of Opuntia constitute a serious weed. At "Westward and 

 Rockhampton, Queensland, where the cacti are particularly a 

 nuisance, over 50 per cent, of the annual rainfall occurs in 

 December-March, inclusive. Soil temperature data from Bris- 

 bane, depth one foot, show that the mean temperature from 

 October to April is between 22.7° and 27.9° C, and that during 

 the colder portion of the year the mean temperature at that depth 

 is below 20° C. 6 



The commission studied the cactus problem in several different 

 portions of the world, among which were Cape Colony, central 

 and southern India, southeastern and southern South America 

 and the Mediterranean region. It will be instructive to sketch the 

 leading climatic features of definite localities where cacti were 

 found to have escaped cultivation. 



In southern Africa, species of Opuntia occur in a naturalized 

 condition in the Great Karoo and in the Transvaal. In parts of 

 the former region, as at Graaf Reinet, the species are abundant. 

 At Graaf Reinet, according to Knox, 7 where the total precipita- 

 tion is 15.29 inches, 63 per cent, occurs in November-March. In 

 the Transvaal, where the escaped cacti are less numerous, the 

 rainfall is 26.94 inches, of which 81 per cent, occurs in November- 

 March. 



In northern Africa the cacti escape from the oases very little, 

 and the same is to a degree true of other portions of the Mediter- 

 ranean region. In Algeria and Tunis, according to Knox, the 

 rains are almost exclusively restricted to the winter season. 



In India species are naturalized over a large territory, as, for 

 example, in the Madras Province and in the Panjab. In Madras 

 the prickly-pear has become a formidable evil throughout several 

 districts. At Madras 8 79 per cent, of the total precipitation takes 

 place in August-September. In the state of Mysore, also, the 



s Report of the Prickly-pear Traveling Commission, Brisbane, 1914. 



e "Results of Rainfall Observations made in Queensland/' H. A. Hand, 

 1914. 



7 "The Climate of the Continent of Africa," 1911. 

 sHann, " Handbuch der Klimatologie, " I. c. 



