[Illustration: Fig. 31. Wheat growing in soils supplied from below with water. All the water the plant gets has to travel upwards] Thus we shall expect great differences in the moisture of various soils. In some districts there is much more rain than in others, and therefore the soils get a larger supply of water. Sandy soils allow water to run through while a loam holds it like a sponge, in a loam also the water readily moves from wet to dry places. Further, water runs down hills and collects in low-lying hollows or valleys; here, therefore, the soil is moister than it is somewhat higher up. What will be the effect of these moisture differences on plants? You must find out in two ways. Visit a soil that you know is dry--a sandy, gravelly or chalky soil in a high situation--and look carefully at the plants there, then go to some moister, lower ground and see what the plants show. You cannot be quite certain, however, that anything you see is simply due to water supply, because there may be other differences in the soil as well. So you must try the second method, and that is to find out by experiments what is the effect of varying {69} quantities of water on the plant growth. Both methods must be used, but it may be more convenient to start the experiments first, and while they are going on to collect observations in your rambles. [Illustration: Fig. 32. Mustard growing in soils supplied with varying quantities of water. 16 very little water, 3 a nice amount of water, 15 too much water] 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; {70} 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