Transpiration as a Factor in Crop Production. 
205 
ADAPTATION OF PLANTS. 
The production of plants adapted to meet the requirements 
for a low transpiration rate offers a field of great possibilities. 
Under this may be included the testing and selection of estab- 
lished varieties already well adapted, and also the selection, with- 
in a variety, of strains possessing certain characters, or the 
creation by breeding of new characters correlated with low 
relative water consumption. It is well known that some plants 
are especially adapted to dry and others to humid conditions. 
For instance, the grain sorghums are well suited for dry farming. 
Just what characters fit them for this purpose is not fully known. 
Results with two of these crops, Milo and Amber sorghum, 
reported in this bulletin indicate that these crops do not have a 
lower water requirement in the production of dry matter than 
does corn under favorable moisture conditions. The work to date 
has been too limited to draw final conclusions. It may be pos- 
sible that these dry land agricultural plants approach the con- 
dition of the desert plants described by Fitting (1911), which 
possess a high osmotic pressure and are able as a consequence to 
extract moisture from a comparatively dry soil in which the water 
films are very thin. Experiments have now been planned which 
should give definite information concerning this. It is evident 
from relative histological studies of the leaves of several sorghums 
and corns that the former have no special leaf structural adapta- 
tion for reducing the transpiration below that of corn. It has 
been observed under field conditions that sorghums appear to 
possess the power of entering into a more or less dormant stage 
when growth conditions become very unfavorable, as in time of a 
very dry spell, and renew growth without having been greatly 
injured when rains come. A plant possessing this power would 
have a great advantage. Frequently, under Nebraska conditions, 
several days of very severe dry, hot, windy weather may greatly 
reduce the yield of corn, because the evaporation rate is more 
rapid than the roots can supply, due to low soil-moisture content, 
and the corn plant is unable to go thru such a period without 
injury. It is these few outstandingly severe days that are espec- 
ially injurious to most crops. 
Merely to know the water requirement per pound of dry matter 
is not necessarily an index as to whether a crop is suited to drouth 
conditions. A kind of crop with a relatively high water require- 
ment per pound of dry matter may normally produce a small 
tonnage per acre, and consequently the total water transpired 
be no higher than with another kind of crop having a relatively 
low water requirement. 
