^5° 



Journal of Agriculture^ Victoria. [lo June, 1912. 



this is done on the scales. At watering, the loss of weight since the 

 previous watering is noted down, and the pot is then brought up to its 

 standard weight again by adding more water. The water lost from a 

 cropped pot will include water transpired by the plant, also water 

 evaporated directly from the soil. The latter is most simply discounted 

 by setting up similar pots without a crop, and deducting the losses there 

 from the losses on the cropped pot.x throughout the season. In transpira- 

 tion experiments the pots must be protected from rain in order to reserve 

 control of the water supply. This is usually done by placing the pots on 

 low trolleys standing on rails, so that they can be run under cover at 

 night and on wet days. 



Proceeding on the general lines of investigation indicated, the following 

 results have been obtained by different workers : — 



Table I. 



Wheat 

 Barley 

 Oats . 

 Rye . 

 Maize . 

 Beans . 

 Peas 

 ■Clover 

 Buckwheat 

 Rape . . 



Lawes (1) 

 (England). 



247 

 2.57 



209 

 259 

 269 



Hellriegel (2) 

 (Germany). 



338 



37 (J 

 353 



282 

 273 

 310 

 363 



329 



(1) Jour. Horticultural Soc, V. (1850). 



(2) Grundlageu des Ackerbaues, p. 622, et seq. 



(3) Bep. Wisconsin, Expt. Stn., 1894, p. 248. 



(4) Mem. Dept. Agric, India. Chemical series. Vol. I., No. 8, p. 179. 



The figures state the transpiration ratios found by different observers. 

 Before going on to discuss them, it is necessary to glance briefly at the 

 uses of water to the plant. 



Water enters the plant body by tlie roots, passes upwards through the 

 stem, and is evaporated by the leaves during transpiration. In its passage 

 through the plant, the water performs certain useful work. It carries 

 dissolved phosphates, nitrates, &c., from the soil into the plant; it is 

 necessary for the life and growth of the protoplasm or living part of the 

 plant, and for the action of ferments ; a small part of the water absorbed 

 ■enters chemically into organic material in the process of carbon assimi- 

 lation. 



Carbon assimilation is the process whereby green plants feed from the 

 carbon dioxide gas of the air and from water. About 95 per cent, of 

 the dry matter of crops is formed from air and water in this way. 



It is difficult to say in which of its uses to the plant it becomes neces- 

 sary that so much water should pass through it during the period of 

 growth. The inward passage of soil constituents probably does not alto- 

 gether require it, as the water current and the soil nutrient movement are 

 within inside limits independent. It is more likely that the partial 

 parching of a crop restricts growth, in the first instance, by increasing the 



