ACID ACCUMULATION IN SUCCULENTS 



265 



from the source of soluble carbohydrates, receive their supply- 

 slowly and are therefore limited to a smaller carbohydrate metab- 

 olism, so that acid production is less rapid than near the surface. 

 Furthermore, as the center of the plant is approached, the in- 

 creasing insulation tends to minimize temperature and light dif- 

 ferences of night and day. Briefly stated there is a large accu- 

 mulation of acids during the night in the outer parts and a large 

 destruction of acids during the day, so that diurnal differences in 

 acidity are large, while in the inner parts there is much slower 

 formation of acids and only a slight diurnal difference in the 



TABLE 2 



Showing differences in the acidity of sap in samples taken in afternoon and 

 morning at different depths from plants of Carnegiea collected July 18 



action of light and heat upon them, so that diurnal differences 

 here are small. 



In the protocols to follow it will be seen that the same condi- 

 tions exist in the bisnaga (tables 4 and 5). 



The facts expressed in the accompanying tables agree in the 

 main with those outlined above in the case of the sahuaros. 

 Bisnagas 28, 29, 32 and 33 are distinctly more acid in the early 

 morning than in- the late afternoon and with only one partial 

 exception the difference in acidity of corresponding samples 

 of the two periods progressively becomes smaller as the cen- 

 ter of the plant is approached. In bisnaga 29 the increase 



