Transpiration as a Factor in Crop Production. 29 
of more than 100 varieties at Akron, Colorado, and also a number 
of varieties in other localities. Regarding the number of plants 
in a potometer, these investigators state (1913, p. 10) that 20 
small-grain, 8 sorghum, 6 corn, and 6 sugar beet plants were 
grown. The potometers all contained 115 kilograms of soil. 
This provides approximately the same amount of soil for three 
small-grain plants as for one corn plant. Under eastern Colorado 
farm conditions approximately 50 seeds of wheat are planted on 
an area of land equal to that occupied by one corn plant. 
Speaking in a general way, it may be concluded that Briggs 
and Shantz grew six corn plants in a potometer where they should 
have grown one, and in proportion to corn they grew 20 wheat 
plants when they should have grown 300. 
Altho Briggs and Shantz were of the opinion that cans of the 
size used by them were of adequate size to allow normal develop- 
ment of the plants, it appears from their illustrations and tables 
that at least the corn and grain sorghums were very much 
underdeveloped, the corn more so than the sorghums, however. 
The total yield per potometer of dry matter from the six corn 
plants is about equal to what the yield from one plant of the 
larger varieties should have been. 
Briggs and Shantz (1913a, p. 18; 1914, p. 5) concluded from 
tests with Kubanka wheat in 1911 and 1912 that the soil used by 
them bore sufficient fertility for normal development. The 
fertilizer application increased the actual yield of dry matter 9 
per cent in 1911 and reduced it 3 per cent in 1912. In 1911 the 
water requirement of the unfertilized set was 6 per cent above 
the fertilized set, and in 1912 it was 4 per cent below that of the 
fertilized set. While these tests show little need for fertilizer on 
the part of the wheat, they do not indicate what would have been 
the result on corn planted at a relatively much thicker rate. 
The effect of overcropping upon the water requirement per 
unit of dry matter is much less marked than the effect upon the 
amount of dry matter itself. (See Table 4 of this bulletin.) This 
general problem of adjusting the number of plants to be grown 
in a unit mass of soil needs further investigation. 
LIMITATION OF SOIL FERTILITY. 
In certain lines of investigation the degree of soil fertility may 
become an important source of error. The principle is again 
involved that the ratio of water loss to dry matter is increased 
as the soil fertility is decreased below a normal range. In an 
experiment to determine the relative water requirements as related 
to the difference in climate of two distinct regions of the country, 
it is essential to use soils of equal productivity in both regions. 
