272 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
tive in reducing the growth and development of other weeds than 
Brassica. According to Brenchly, mustard would then, even in 
moderate amounts, do considerable damage. Gates and Cox 7 
have arrived at the conclusion that weeds make the cultivation of 
corn necessary. 
Possibly in the majority of places, even in the agricultural 
areas of the Middle West, there are times in which there is not 
enough water to supply the needs of the plant. Water is used 
by a plant in large quantities and practically all of it passes off 
in the transpiration stream. Water is an important item and its 
conservation is a question with which we must be concerned. 
From the few citations given above it is evident weeds do con- 
siderable damage to growing crops by consuming the moisture. 
Knowing that transpiration or the giving off of water by the 
aerial portions of a plant goes hand in hand with the leaf area, 
a study in which the leaf area and transpiration are measured 
from time to time at specific intervals should give us much in- 
formation concerning the effect of weeds upon the crop with 
which they are associated, both in the greenhouse and in the field. 
GREENHOUSE. TESTS 
In a rather extended series of experiments regarding the real* 
status of the question as to the nature of the competition between 
mustard ( Brassica ) and wheat and oats which were performed in 
the Botanical Laboratories at Iowa State College, an attempt 
was made to determine the amount of water used and the amount 
of leaf tissue formed, from the time the seedlings appeared, until 
the grain was mature. In these series of experiments four cul- 
tures were given over to wheat, four to oats, one to mustard 
alone and finally one culture contained only soil. Each of the 
ten cultures was contained in a galvanized pail 25 by 20 cm. in 
size, and was made up as follows : 
/. WHEAT SERIES 
Culture No. 1. Wheat — 7 plants. 
Culture No. 2. Wheat and mustard — 5 plants of wheat, 4 plants of 
mustard. 
Culture No. 3. Wheat — 10 plants. 
Culture No. 4. Wheat and mustard — 10 plants of wheat, 2 plants of 
mustard. 
7 Gates, J. S., and Cox, H. R., The weed factor in the cultivation of corn: U. S. 
Dept. Agric., Bureau PI. Ind. 257. 
* These experiments were made largely by Mr. H. H. Plagge of the Pomology Sec- 
tion of the Iowa Agricultural Experiment' Station. He was, at that time, a Fellow 
in Plant Physiology. 
