73 
The Effect of Weeds upon Cereal Crops. 
The plants were grown in bottles of 600 c.c. capacity ; after 
three weeks extra ferric chloride was added at the rate of 
0-02 grams per litre, and at the end of five weeks the food 
solutions were completely renewed. Two plants were grown in 
each bottle, the corks being bored with two holes and cut into 
three pieces in order to accommodate the plants. Wheat 4- wheat, 
wheat + weed, weed + weed were tested in each of two sets of 
experiments, the weeds being Spergula arvensis and Alopecurus 
agrestis. In every case ten bottles were grown with a similar 
combination of plants. 
Wheat and Spergula arvensis. 
Wheat seed, graded 006—0 # 07 gram., sown April 4th. 
Spergula sown April 3rd. 
Plants put into solution April 15th. 
The wheat grew well from the beginning, either alone or with 
spurrey. After two or three weeks the double wheat plants were 
yellowish, but they soon recovered on the addition of extra iron. 
The plants associated with spurrey were much less etiolated at the 
some time. All the wheat remained strong and healthy until 
harvested. 
The Spergula started into growth quite well in both cases, 
but within three weeks a difference manifested itself. The double 
plants were fine and healthy, had made strong growth, and had 
nearly all developed two whorls of leaves. The single plants, with 
wheat, were much less strong, and most had only formed one 
whorl of leaves. If two were present the upper whorl was weak. 
Apparently the overshadowing of the wheat had begun to affect 
growth. Before the close of the experiment on July 4th, all the 
spurrey plants, whether alone or associated, had died off without 
making much more growth. This may have been due to a 
temperature factor, as some very hot weather was experienced. 
It was impossible to disentangle the roots of the plants, so that 
unfortunately it was necessary to dry and weigh the roots of the 
two plants from each bottle together. 
Great variation was observed in the weights of the different 
pairs of plants, the variation being much more marked than is 
usual in water cultures when plants are grown singly under similar 
conditions. The results were as follows:— 
