512 
Philippine Journal of Science 
1920 
latively very dry, as compared with active plant tissues in gen- 
eral, and that the drying of leaf tips that occurred in many of 
the poorer cultures was without marked effect upon the per- 
centage of water content. 
In considering the green weight as a criterion for comparing 
the physiological efficiency of different cultures, etc., it should 
be remembered that there is probably a more or less pronounced 
daily fluctuation in the water content of leaves and small stems, 
as has been emphasized by Livingston and Brown,®° by Renner,®^ 
by Edith B. Shreve,®^ by Yuncher,®® and by others. 
Water absorption . — The four simultaneous series carried out 
in the period beginning June 19 (series 14, 16, 19, and 20) also 
furnished comparative data on water absorption, which are 
presented in Table 13. These values are the amounts of water, 
in cubic centimeters, absorbed during the entire culture period. 
Considering the very small amount of water retained by the 
plants (see the green weights and dry yields of tops), the ab- 
sorption values clearly represent the amounts of water tran- 
spired, which, as Livingston ®^ has shown, may be generally con- 
sidered as an approximate index of the leaf area, at least for 
young wheat plants. In studies like the present one the use of 
the total amount of water transpired during the growth period, 
as a criterion for comparing the plants of different cultures, seems 
to have been inaugurated by Whitney and Cameron,®® and it has 
been continued by Livingston, Britton, and Reid,®® and by many 
other later workers. It appears that Shive (1915) was the first, 
at least among those who have been engaged in the recent sys- 
tematic study of salt relations by the method of solution cultures, 
to employ water absorption instead of transpirational water loss. 
Since this gives another quantitative criterion by which plants 
Livingston, B. E., and Brown, W. H., Relation of the daily march of 
transpiration to variation in water content of leaves, Bot. Gaz. 53 (1912) 
309-330. 
'"Renner, 0., Beitrage zur Physik der Transpiration, Flora 100 (1910) 
451-547. 
Shreve, Edith B., The daily march of transpiration in a desert peren- 
nial, Pub. Carnegie Inst. Washington (1914) No. 149. 
^“Yuncher, T. G., A study of the relation of soil moisture to transpira- 
tion and photosynthesis in the com plant. Plant World 19 (1916) 151-161. 
Livingston, B. E., Relation of transpiration to growth in wheat, Bot. 
Gaz. 40 (1905) 178-195. 
“ Whitney, M., and Cameron, F. K., Investigation in soil fertility. Bull. 
U. S. Dept. Agr., Bur. Soils 23 (1904). 
*“ Livingston, B. E., Britton, J. C., and Reid, F. R., Studies on the prop- 
erties of an unproductive soil. Bull. U. S. Dept. Agr., Bur. Soils 28 (1905) 
39. 
