CHAPTER VII. PLANT NEEDS. Plants need water, air, food, light and warmth just as animals do, and it is wonderful to study the shifts and contrivances to which they resort to get these, and also to protect themselves against too much of any of them. If the plant were not able to change itself to suit the conditions, it would often die where now it fights successfully. Nothing affects the plant like the water supply; the size of every part of the plant is increased by plenty of water. It not only helps the growth of flowers and fruits, but it even changes the character of the plant. In a moist air, cactus will put out leaf-like organs, gorse will grow leaves instead of thorns; while where the water supply is very scanty, the potato will put forth no leaves, but will become like a cactus. Yet plants do not grow in soil that is too wet, because they need air, and too much water suffocates the roots. By proper irrigation—which means giving just the right supply of water—both the quantity and quality of the crop can be improved. While plants need light, all varieties do not need the same amount of it. You will find that those which need much light can turn towards it, and this of itself will show you where such plants should be sown. Plants have various ways to resist the supply of light when they are getting too much. They droop their heads or close their leaves, which prevents evaporation. Different plants need different food and the same soil conditions will not suit all. Some require rich soil if they are to flourish, while some do better in poor soil. On the whole, plants, like people, are better for under-feeding than for over-feeding. In general, starving a plant makes it flower and fruit more quickly, but less abundantly; while over-feeding helps to make much stem and leaf instead of fruit, and also produces monstrosities. Too much nitrogen, especially, makes too much stem and leaf, though nitrogen is one of the most important plant foods. (Bailey says too much nitrogen can be corrected to a certain extent, by potassium put in the soil.[3]) We are sure of only three plant foods—potash, phosphoric acid, and nitrogen. Then there are lime, stable manure, green manure, clover and cowpeas to doctor the soil with, when it is suffering from chemical ills. This gives some idea of the vast unexplored regions of agriculture which afford you and every other worker in the soil an opportunity to make some great discovery for the benefit of the world. No other calling offers such limitless opportunities.