INJURIOUSNESS OF WEEDS 673 



tree is also stated to transpire 10 to 20 gallons of water in a day; 

 while barley, beans, and clover were found to transpire, during 

 five months of their growth, over 200 times their dry weight of 

 water. Experiments conducted at the agricultural experiment sta- 

 tion of Cornell university showed that during the growth of a 60- 

 bushel crop of maize the plants pumped from the soil, and tran- 

 spired into the air through the leaves, upwards of 900 tons of 

 water. A 25-bushel crop of wheat similarly disposed of 500 tons of 

 water. Weeds also transpire, and if the ground be covered with 

 weeds it is certain that much of the moisture which would be of 

 value to the crop will be lost in the manner indicated. Weeds are 

 especially harmful in this way in a hot summer, and the loss is 

 most felt by the cultivated crop on light sandy soils. 



3. WEEDS CONSUME MINERAL AND FOOD ELEMENTS. 



A weed needs not only the carbon dioxide of the air to make 

 food, but the nitrogenous and mineral elements of the soil to make 

 plant food, all of which should go to the crop. Long gives the fol- 

 lowing in his book, "Common Weeds of the Farm and Garden": 



Some analyses made at Konigsberg, and lately reported by Profes- 

 sor Stutzer and L. Seidler, show that the amounts of nitrogen, phos- 

 phoric acid, potash, and lime which are removed are deserving of 

 serious consideration. A number of weeds without their roots were 

 collected from oat fields, the soil of which was fairly heavy and 

 poor in humus. In the case of the Wild Radish or White Char- 

 lock the plants had already formed many seed-pods, but the other 

 weeds were in full bloom. The table following shows the percentage 

 of ingredients in the dry matter. These figures indicate in a gen- 

 eral way the amount of the chief plant foods required by weeds. The 

 nitrogren in the Persicaria nearly equaled 20 per cent, and that in 

 the Sow Thistle nearly 15 per cent of albuminoids in the dry mat- 

 ter. Phosphoric acid was chiefly taken up by Spurrey and Persi- 

 caria; potash by the Sow Thistle and Spurrey; and lime by Per- 

 sicaria, Yarrow, and Cornflower. 



43 



