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to their state of maturity. According to Professor King, of Wis- 
consin, it requires 300 to 500 lbs. of water to produce lb. of dry 
vegetable material, or in other words, to produce 1 ton of hay, it 
is necessary to have 300 to 500 tons of water, which must be sup- 
plied by rain or by irrigation during the growing period; so it 
1 ton is to be grown on an acre there must be from 3 to 5 inches 
of water supplied at the proper time. (The weight of 1 inch of 
water over 1 acre of land approximates 100 tons.) It is essential that 
the contents of the cells which enter into the structure of the grow- 
ing plant should be in a half-liquid condition in order that nourish- 
ment and construction material should be carried and distributed 
wherever required, be it in the stem, the tender buds, or the ripening 
fruit. When the cells cease to be distended with fluid sap they zet 
flaceid and the plant wilts. Unless this state is promptly remedied 
by an influx of sap these cells thicken, they lose their elasticity, 
the lant first gets stunted and finally dries up and dies. The water 
necessary for plant growth is absorbed by the hair-like rootlets 
issuing from the stronger roots which penetrate the ground in search 
of food and moisture; it does not, however, enter into the cireula- 
tion of plants quite pure, but contains in solution variable quanti- 
ties of substances which plants feed upon. From these rootlets it 
is passed on from cell to cell, by a process of diffusion, first along 
the larger roots which anchor the plant to the ground, thence to the 
stem, on to the branches, the buds, leaves, and fruit. 
That cell to cell motion, or that diffusion of the nourishing 
sap, from the capillary rootlets to the tip of the branches, is quick- 
ened by evaporation. 
The evaporating organs of the plants are the leaves. These, 
when fanned by the breeze, allow a considerable amount of mois- 
ture to escape through the stomata or breathing pores. In bright 
daylight these pores open to allow the admission of carbon and of 
oxygen to the working cells of the leaves. As this takes place a 
good deal of the moisture which saturates the air in the intercellular 
spaces of the leaves escapes to the drier outside air. A vacuum is 
thus created, and more moisture exudes from the gorged cells to 
replace the amount lost through evaporation. In this manner a 
current of sap is created from the rootlets upwards towards the 
branches. 
Under certain circumstances this current may run quicker than 
the plant is able to absorb moisture from the ground. This is 
noticeable on a dry, hot day, when the plant flags. 
This being so, it is easy to understand that other conditions 
of soil texture and of particular plant requirements being alike, a 
given field crop, or trees of the same sort and age, wiil show signs 
ot wilting and need for water much sooner in the drier air of the 
inland districts than in the moister air of the coastal zone. In both 
instances the soil may have been wetted to saturation, point by the 
