86 KDiir ii.Murs m- I)i:si:kt I'i.a.ms. 



the line sc-paratinj; llie two. TIr- nsiilts of this culture have already Ik'ch 

 given above and need only be summarized here. 



The plant on the adobe-clay side of the culture had develojied two sorts 

 of roots: a lleshy tap root which inclined away from the water jK)le and 

 ended in a curl, and several of llie usual sort (plate 23). The bulb had 

 entirely disappeared. The plant on the sand side of the box (both were 

 very close to the opposite kind of soil) had developed two kinds of roots 

 also, a large tap root and a few laterals. The tap root went straight down 

 without regard to the water pole (plate 2,^). In the latter plant the bulb 

 had not wholly disappeared. 



In connection with the behavior of the Ihodiaa, whatever may be the 

 immediate underlying causes, it is of interest to review the reaction of 

 certain cacti to analogous natural and cultural conditions. In the course of 

 observations on the roots of the cacti it was learned that frequently the 

 seedlings of the arborescent forms were provided with fleshy roots, and also 

 that in the root-systems of the mature plants of Ofyiintia vh'ipara some 

 of the roots were slender and some fleshy, and also that all of the laterals 

 of Opuntia arbuscula were fleshy. In the latter species the description 

 applies onlv to the plants from near Tucson: those seen near Sacaton 

 are slender throughout. Cultures of cuttings from the Sacaton form of 

 arbuscula, the Tucson representative of the same species, and of Opuntia 

 vivipara, were grown in the experiment house during the spring and sum- 

 mer. The soil in which the plants were placed was sand and adobe, about 

 equal parts. The culture was frequently watered throughout the entire 

 period. On November 21 the plants were carefully removed from the soil 

 and it was noted that all of the larger roots of O. vivipara were fleshy; the 

 longer roots of the arbuscula from Sacaton, the species which does not pos 

 sess fleshv roots in its natural surroimdings, were fleshy also, as were those 

 of the specimens from Tucson. Bv:t the fleshiness of the last was the least 

 marked of anv (plate 21). It would appear, therefore, that the character 

 of fleshiness in these cacti and in Brodicra is to be associated with an 

 abundant water supply. 



Besides ser\^ing as water-storage organs the fleshy roots of Opuntia 

 arbuscula. from Tucson, also propagate the species, as mentioned above 

 and described bv Preston (Non-sexual propagation of Opuntia, Bot. Gaz., 

 p. 128, vol. 31, 1901). This appears to be a very common way of increas- 

 ing the number of individuals. To learn whether similar conditions 

 might obtain in those roots of 0. vivipara which were tieshy, one was brought 

 to the experimental plantation and given water freely for some months. 

 From this root a single well-developed shoot with roots appeared and con- 

 tinued to grow vigorously (plate 21 "I. 



