Fill four glazed pots with dry soil: keep one dry; one only just moist; the third is to be very moist and should be watered more frequently than the second; and the fourth is to be kept flooded with water, any way out being stopped up. Sow wheat or mustard in all four and keep out of the rain. The result of one experiment with mustard is shown in Fig. 32. Where no water was supplied there was no growth and the seeds remained unaltered. Where only little water was supplied (Pot 16) the plants made some growth, but not very much: the leaves were small and showed no great vigour; where sufficient water was given (Pot 3) the plants grew very well and had thick stems and large leaves; where too much water was given (Pot 15) the plants were very sickly and small.
The weights were:—
Green weight After drying
Plants with too much water 3.9 0.5
" " too little water 5.3 0.9
" " a nice quantity of water 17.7 2.6
Fig. 33 shows two pots of wheat, one kept only just sufficiently moist for growth, the other kept very moist but not too wet. You can see what a difference there is; in the drier pot the leaves are rather narrow and the plants are small, in the moister pot the leaves are wide and the plants big. But there was also another difference that the photograph does not bring out very well—the plants in the rather dry soil were, as you can see, in full ear, ripe and yellow, while those in the very moist soil were still green and growing. We see then
(1) that on moist soils there is greater growth than on dry soils, but the plants do not ripen so quickly;
(2) in very wet soils mustard—and many other plants also—will not grow.
Water is not itself harmful. It is easy to grow many plants in water containing the proper food, but air must be blown through the water at frequent intervals. In the water-logged soil of Pot 15 the trouble arose not from too much water but from too little air. Air is wanted because plants are living and breathing in every part, in the roots as well as in the leaves.
