46 WATER-RELATION BETWEEN PLANT AND SOIL. 



have furnished a rather complete history of the march of the water 

 relations for the entire life of the plants. As it is, the introduction of 

 the method of relative values on the same basis, for two days a month 

 apart, has for the first time furnished evidence on the fluctuation in 

 transpiring power (or relative transpiration), and on that in absolute 

 transpiration, which occur during a month in the middle of a plant's 

 life. The transpiring power of all these plants proved thus to be very 

 markedly less for the 24-hour period in March than for a similar period 

 in February. Our plants were practically full grown at the earlier time 

 and the effect of increase in size (with its concomitant increase in leaf 

 surface) was apparently much more than offset by some process of 

 maturation within the plant, as the hardening of the leaves. The 

 question thus suggested, of the march of transpiring power throughout 

 the life history of the plant, is worthy of further study, and this matter 

 will require consideration before the relations of water, salt, and other 

 requirements at different stages or phases of the plant's growth (rela- 

 tions so important to agriculturists) may be placed upon a satisfactory 

 foundation. It seems quite futile, for example, to expend time and 

 energy in the quantitative comparison of the mineral requirements at 

 different ontogenetic stages, so long as the water-relations of soil, air, 

 and plant are ignored, as has been done so frequently. 



The last remark is representative of a legion of fundamental inade- 

 quacies prevaiUng in present-day methods of physiological study, 

 inadequacies which want only attention to be very largely removed. 

 What appears to be needed to place physiological and ecological 

 reasoning upon the same logical basis as that on which rest the more 

 fundamental physical sciences seems to be, for the present at least, 

 the application here of what knowledge and methods those sciences 

 have already developed. Sooner or later it may be realized that the 

 behavior of an organism is not to be adequately studied without quan- 

 titative knowledge of its surroundings, just as it is now commonly 

 accepted that a physical or chemical determination is without great 

 value until the environmental conditions and the apparatus used have 

 been subjected to at least as penetrating scrutiny as that directed to 

 the phenomenon in question. This paper has aimed to present what 

 appear to be several short steps in this general direction toward a 

 quantitative appreciation of the water-relations between the plant and 

 its surroundings. 



