168 INSECT PESTS 



little cells. All plants and animals are built up of 

 cells, which are constantly wearing away and as con- 

 stantly being renewed and increased. When the 

 creature fails to renew its waste tissue, it dies and falls 

 into complete decay, reverting to the original elements. 

 It is therefore vital that this renewal and re-forming 

 of cells should be understood and assisted in every 

 way. Cells are filled with protoplasm, a mucous or 

 gelatinous substance composed of water, carbon, 

 nitrogen and sulphur, which Huxley called "the 

 physical basis of life." This apphes to both the 

 animal and the vegetable kingdoms. Vegetables are, 

 however, distinguished from animals as a rule by the 

 fact that their cells are always enclosed in a definite 

 and comparatively solid box or cell-wall, made of 

 cellulose, the raw material out of which every plant 

 structure, from the tiniest blade of grass to the noblest 

 cedar pine, is built. Cellulose can be chemically reduced 

 to merely carbon and water, although no scientist has 

 yet been able to change these elements back again 

 into cellulose. The same remark might of course apply 

 to cane sugar, which is of exactly the same composition, 

 and if it had been easy to recompose it we should not 

 have had to present our grocer with a carefully guarded 

 coupon week by week, but that is by the way. 



We see then that plants are mainly composed of the 

 elements Carbon, Hydrogen, Ox.ygen, Nitrogen and 

 Sulphur, and if we think of the initial letters of these 

 substances, C.H.O.N.S., it will help us to remember 

 it. There also occur small traces of Iron, Magnesium, 

 Phosphorus, and Salt (sodium chloride), as well as 

 Silicon. These are the I.M.P.S., which dwell in the 

 soil, and good little imps they are, for when the 

 ground is properly tilled, the oxygen from the air 

 combines with them to form important plant foods. 



Now, how does a plant feed ? Here is our bean 

 growing away merrily, if you like, in an observation 



