=156. The quantitative relation of absorption and transpiration.= Burgerstein[11] has summarized the results of various investigators in the statement “that between the quantitative absorption of water on the one hand and emission on the other there exists no constant parallelism or proportion,” and he has cited the work of Kröber, and of Eberdt in proof. This statement holds, however, only for short periods of a few hours, or more rarely, a day, and even here its truth still remains to be conclusively demonstrated. The discrepancy between absorption and transpiration for a short period is often greater than for a longer time, but it is evident that a transient change in behavior or a small error in the method would inevitably produce this result. Eberdt found the discrepancy for a few hours to be 1–2 ccm. in an entire plant of _Helianthus annuus_, while for a whole day the water absorbed was 33.57 ccm. and the water lost 33.98 ccm. Kröber’s experiments with cut branches of _Asclepias incarnata_ showed a maximum difference for 12 hours of 2.5 ccm., but the discrepancy for the first 24 hours was 1 ccm. and for the second 1.9 ccm. In both cases, the potometer was employed. Consequently, as will be shown later, Eberdt’s results are not entirely trustworthy, while those of Kröber, made with cut stems, are altogether unreliable. Hence, it is clear that the discrepancy is slight for a period of several days or weeks, and that it may be ignored without serious error, except in a few plants that retain considerable water as cell-sap, in consequence of extremely rapid growth. Accordingly, the amount of transpiration, which may be readily and accurately determined, can be employed as a measure of absorption that is sufficiently accurate for nearly all purposes. The truth of this statement may be easily confirmed. It is evident that the amount of water absorbed equals the amount transpired plus that retained by the plant as cell-sap, or used in the manufacture of organic compounds. In plants not actively growing, the amount lost equals that absorbed, as already shown in the experiment with _Helianthus_. According to Gain[12], Dehérain has found that a plant rooted in ordinary soil transpired 680 kg. of water for each kilogram of dry substance elaborated. In _Helianthus annuus_, the dry matter is 10 per cent of the weight of the green plant. A well-grown plant weighing 1,000 grams, therefore, consists of 100 grams of dry matter and 900 of water. The length of the growing period for such a plant is approximately 100 days, during which it transpires 68 kilograms of water. Assuming the rate of transpiration and of growth to be constant, the plant transpires 680 grams daily, adds 9 grams to its cell-sap, and 1 gram to its dry weight. The amount of water in a gram of cellulose and its isomers is about ⅗. Consequently, the total water absorbed daily by the plant is 689.6 grams. The 680 grams transpired are