26 SOME EEATURES OF PLANT GROWTH. 



plant tends to regalate the temperature. Evaporation is a cooling 

 process, and as this is constantly taking place from the surface it 

 has much to do with keeping' the plant cool in the presence of direct 

 sunlight. 



In order to prove that evaporation does take place from the surface of 

 all green plants, take a quart or pint jar, remove the cover and place it, 

 mouth downward over some green grass in the presence of sunlight. It 

 will be found that moisture will collect in the inside of the jar in sufficient 

 quantity to form large drops. 



DRY MATTER. This is the part of the plant that remains after 

 the water is driven off. It is composed of two parts, one of which 

 is given off when the plant is burned, while the other remains be- 

 hind in the form of aslies. 



A very simple experiment will illustrate this point quite clearly. 



Take the dry grass used in the previous experiment and place it in an 

 iron vessel on a stove or in some way bring it in contact with a good fire. 

 It will be found that only a small portion, the ash, remains. 



We spoke about the source of water in plant life. We shall 

 now enquire into the source from which the remaining substances 

 were obtained. We are all well aware that the leaves of plants 

 are constantly surrounded by atmospheric air. This air contains 

 a substance known as Carbonic acid which is taken up by the 

 leaves, of the plant and becomes part of the structure of the leaves, 

 stem, and root. The carbon taken from this source forms about 

 half of the dry matter of the plant. Oxygen, Nitrogen, and Hy- 

 drogen are other elements that enter into the composition of the 

 part of the plant that burns. The first of these is taken partly 

 from the soil, being contained in the water that surrounded the 

 roots. The ash, or that portion of the plant remaining after burn- 

 ing, forms but a small portion of the entire plant. It is composed 

 of iron, potash, lime, magnesium and phosphoric acid. These 

 form, as it were, the frame work around which the whole fabric of 

 the plant is constucted. They are usually present in soil water, 

 and enter the plant through the medium of the roots. The pre- 

 sence or absence of these substances in suitable form constitutes 

 the difference between a rich or poor soil. 



From what has been said it will be observed that the food ma- 

 terials enter the plant in the form of a fluid, either a liquid as water, 

 or a gas as carbonic acid and oxygen. It was long thought that 

 small particles of the soil entered the roots, but it is now known 

 that this is not the case. 



