B. 1'. I. Bi 
THE WATER REQUIREMENT OE PLANTS. 
II— A REVIEW OF THE LITERATURE. 
INTRODUCTION. 
The review of the literature relating to the water requirement of 
plants here presented was begun in connection with the writers' 
investigations on this subject in the Great Plains. The literature 
proved to be much more extensive than was anticipated, and it has 
consequently seemed desirable to present independently a summary 
of the investigations bearing on this subject, particularly since some 
of the papers are not readily accessible and since a review oi the whole 
subject has apparently not been undertaken heretofore. In reviewing 
the papers it has appeared desirable to group them with reference to 
the various factors which affect the water requirement. When more 
than one phase oi the subject is dealt with in the same paper, the 
special material relating to each phase of the work has been con- 
sidered in its appropriate place. In summarizing the papers the 
endeavor has been to give in tabular form the essential data of each 
investigation. This will enable the reader to draw his own conclusions 
from the experimental results independently of any interpretation 
which the writers may have given. 
Among the different subjects which have been investigated in 
relation to their effect upon the water requirement may be mentioned 
soil-moisture content, type of soil, cultivation, amount of soil used, 
fertilizers, temperature, light, humidity, carbon-dioxid content of 
the air, relative leaf area, defoliation, and duration and period of 
growth, as well as the water requirement of different kinds of plants 
when grown under comparable conditions. The division of the sub- 
ject into these groups has been largely determined by the character 
of the investigations which have so far been made, and is not pre- 
sented as an ideal division of the water-requirement problem. The 
papers which deal with any of the above phases of the water-require- 
ment problem, so far as the writers have been able to consult them, 
are discussed in the following pages. The full title and reference are 
given under "Literature cited" at the end of the bulletin. The year 
of publication in parentheses in the text following the author's 
1 The preparation of this bulletin was carried on in cooperation at every stage between the Office of 
Alkali and Drought Resistant Plant Investigations and the Office of Biophysical Investigations. The 
authors' names have been placed alphabetically on the title-page. 
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