EFFECT OF WEEDS ON CROPS 
273 
Culture No. 5. 
Culture No. 6. 
tard. 
Culture No. 7. 
Culture No. 8. 
tard. 
II. OATS SERIES 
Oats — 7 plants. 
Oats and mustard — 7 plants of oats, 3 plants of mus- 
Oats — 10 plants. 
Oats and mustard — 10 plants of oats, 4 plants of mus- 
III. MUSTARD SERIES 
Culture No. 9. Mustard — 3 plants. 
Culture No. 10. 
Soil. 
IV. SOIL SERIES 
To determine the amount of water lost during the course of 
the experiment the plants were weighed on small platform scales 
three times a week after February 6. As much water as had 
been transpired each time was added. The soil surface was not 
coated with a wax mixture or plasticine as it was deemed ad- 
visable to permit evaporation to take place unrestricted from both 
soil and plant. After the first month there is sufficient leaf sur- 
face so that the soil evaporation can be considered as negligible 
compared with the amount of water given off by the plant tissue. 
The leaf area was measured at the end of each week by means of 
a polar planimeter. In all cases the leaf area includes both sur- 
faces of the leaf. 
No attempt will be made to trace the different increases or 
decreases during the progress of development. However, the time 
at which the plants of the different cultures attained their max- 
imum, produces a phase of the weed question which has not been 
adequately considered before. The time at which the maximum 
leaf area is formed coincides with the period at which the grain 
is ready to head out. There are no apparent differences in the 
time of maturity. The time for the . formation of the grain is 
then decreased. 
It is apparent that a mixed culture of wheat with mustard and 
of oats with mustard attains its maximum leaf area at a latter 
period than does a pure culture. In the case of spring wheat 
especially, as far as rust is concerned, this item becomes an im- 
portant proposition. It also appears that the same is true for 
transpiration. In culture 6 the maximum transpiration is recorded 
as occurring at the same time as in culture 5. But the mustard 
in culture 6 was completely eliminated, so the culture as a whole 
assumed a condition similar to culture 5 where no mustard plants 
were present. 
