46 



TRANSPIRATION IN A DESERT PERENNIAL. 



TABLE 20. Water content of stems and branches of adult trees. 



Date, Augusts, Wll. 



Experiment XVIII. 



FIG. 22. Graphs of water content measurements taken simultaneously from two adult 

 trees at three different distances from the ends. Graph for relative transpiration of a 

 leafless branch repeated at top of figure. Exp. XVIII. 



EXPERIMENT XIX. 



Subject, the tree from which branches/, g, and h were taken. (See experi- 

 ments XI to XIII.) End twigs about 3 to 5 cm. long were cut off, the 

 leaves quickly severed, and the leaves and twigs placed in separate air-tight 

 shallow weighing-bottles. The bottles with their contents were weighed on 

 good chemical balances to 0.001 gm., and the contents were then transferred 

 to glass beakers and protected from dust, etc., by filter-paper covers. The 

 beakers and their contents were then dried to constant weight in an electric 

 oven at 72 to 75 C. By the use of the above precautions it was possible 

 to obtain the water-content, of the small amount of material which it was 

 necessary to use, accurately to 0.2 per cent. Calculations were made as 

 before for percentage of dry weight of the material used. At noon and at 

 2 p. m. samples were taken from another tree about 30 yards distant. In 

 table 21 these appear under the heading "Series II." 



