THE CAEBOHYDKATES OF THE CACTI. 



39 



IV. THE CARBOHYDRATES OF THE CACTI. 



As has already been indicated, the cacti consist essentially of carbo- 

 hydrate material. Compared to this the protein and fats are present in only 

 small quantities, nor does the content in the plant of these latter substances 



vary appreciably by the change of con- 



TABLE 5. ditions which so decidedly affect the 



carbohydrates. Roughly, the fresh ma- 

 terial of the growing and mature joints 

 is composed about as shown in table 5. 

 Griffiths and Hare 1 give the fol- 

 lowing analysis (table 6) of the ash 

 of Opuntia phceacantha collected in the 

 Santa Rita Mountains near Tucson, 

 Arizona. 



Individual plants show a considerable variation in all their components, 

 depending upon their location and the general complex of environmental 

 conditions. 



The differences in carbohydrate-content and 

 in the proportion of the various sugars be- 

 tween plants growing in the desert at Tucson 

 and in the cool, humid climate of Carmel, 

 California, is illustrated in the accompany- 

 ing analyses of Opuntia ph&acantha during 

 September (table 8). The values are in per 

 cent of the fresh weight. An analysis of the causes which induce these 

 differences in composition will be taken up later. 



For comparison analyses are given 

 in table 8 of Opuntia ptweacantlw, 

 and of Opuntia versicolor, the latter 

 being relatively free of the mucilagi- 

 nous substances so profuse in the 

 former. 



It is evident that the major por- 

 tion of the carbohydrates in these 

 plants is in the form of polysaccha- 



TABLE 6. 



TABLE 7. 



rides and, as will be seen, the simpler 

 sugars (monosaccharides and disaccharides) vary greatly with condi- 

 tions, both in total content and in the proportion to the polysaccharides. 

 A separation of the monosaccharides and disaccharides from the polysac- 

 charides was obtained by means of thorough extraction with alcohol, the 

 first two groups going completely into alcohol, while the latter are insoluble. 

 The acid hydrolysis portion contained the hydrolyzed polysaccharides as 

 well as the monosaccharides and disaccharides. 



1 GRIFFITHS, D., and R. F. HARE. Prickly pear and other cacti as food for stock. Bull. 

 New Mexico Agri. Expt. Station, 60, 15, 1906. 



