TRANSPIRATION AS A FACTOR IN CROP 
PRODUCTION. 
BY T. A. KIESSELBACH. 
PART I. GENERAL SURVEY. 
Such large quantities of water are used in the growth of agri- 
cultural crops that the water supply is frequently a limiting factor 
in production. The importance of proper water relationships has 
long been recognized, and the subject of transpiration is deserving 
of thoro investigation. 
Water taken in by the roots of plants during growth either 
enters chemically into the products of photosynthesis or escapes 
from the above-ground parts of the plant (mainly the leaves) as 
the result of internal and external forces tending to establish an 
equilibrium. The relative amount entering into chemical com- 
bination is negligible. 
The forms in which water escapes from the leaves may be 
classified as (1) water in liquid form and (2) water vapor. The 
former is negligible in amount and results occasionally from in- 
ternal pressure caused by high turgesence, which forces drops of 
water thru minute water pores in the epidermis. The second source 
of water loss, namely, evaporation, practically equals the amount 
taken into the plant, and is caused by the evaporating power of 
the atmosphere adjacent to the leaf. A small amount is evapor- 
ated directly thru the nearly impervious walls of the epidermal 
cells. 1 The remainder is evaporated into the air spaces within 
the leaf from adjoining cells, and is removed thru the stomata in 
Acknowledgment for efficient assistance during the course of these ex- 
periments is made to Messrs. J. A. Ratcliff, C. A. Helm, F. D. Keim, R. E. 
Holland, Ernest Anderson, Bert Danley, E. R. Ewing, and Miss Bessie Noyes. 
References to previous publications from this Station on the subject of 
transpiration are as follows: Montgomery (1910), Kiesselbach (1910), 
Kiesselbach and Montgomery (1911), and Montgomery and Kiesselbach 
(1912). 
Barnes (1910, p. 327) states that, "Of the total water lost, scarcely 
more than 20 per cent and as little as 3 per cent escapes thru the epidermis." 
Barnes does not state how this estimate was obtained. His estimate probably 
covers the extreme range of plants. With our cultivated crops this cuticular 
transpiration probably does not greatly exceed the lower limit. 
