74 PLANT LIFE. 



6. It has to defend itself against the weather (physical 

 conditions) and against vegetable and animal enemies. 



7. It has to reproduce or multiply. 



The special work of the leaf is carbon-assimilation 

 and the supply of energy (3 and 4) ; that of the root is 

 absorption of water and minerals from the soil (2) ; 

 the flower, fruit and colonising arrangements are 

 intended for reproduction (7). Every cell, however, 

 has to carry on respiration (i), support itself (5), and 

 protect itself from its enemies (6). The stem is chiefly 

 for mechanical support. It is under stems also that the 

 food and water distribution are most easily studied. 



Every cell also has to obtain water (from the root) 

 and its carbonic food material (from the leaves). 

 Almost every plant cell consists of a small quantity of 

 protoplasm enclosed in a wall which is built up round 

 itself by the protoplasm. The wall, consists, at first, of 

 a substance, "cellulose," which is secreted by the proto- 

 plasm, and which contains only carbon, hydrogen and 

 oxygen. Within the protoplasm is a mysterious body, 

 the nucleus, that appears to act as the manager of 

 every process that goes on within the cell. A few 

 Algae and Fungi are free and independent, but in all 

 other plants the cells are joined together to make up the 

 plant-body. By this union the cells become dependent 

 on one another, and lose the chance of developing their 

 own individuality, but it is only by the division of the 

 necessary labours amongst them, that it has been 

 possible for complex plants, such as Wheat, Orchids, 

 and forest trees, to come into existence. 



Every plant begins life as a single cell produced by 

 the union of the male pollen grain with the female ^%% 

 cell, and it is by the division of the ^g% cell that the 

 seedling is formed. 



