]

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

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 {71} breathing in every part, in the
roots as well as in the leaves.

[Illustration: Fig. 33. This wheat growing on very moist soil was
still green and growing vigorously, whilst this wheat growing on rather
dry soil was yellow and ripe]

Now turn to what you have seen in your walks. You would probably
notice that on the drier, sandy or