324 HOW PLANTS LIVE AND WORK. 



carbon dioxide at the disposal of the plant, and conversely, plants 

 such as Fungi, which have no chloro[)hyll, are unable, even in 

 sunlight, to separate carbon from the. air. Now, starch, sugars, 

 and a host of other useful and indispensable bodies are made up 

 of carbon united with the elements of water. These substances 

 are manufactured in the leaves of plants. There the carbon from 

 the air, and the water which the conducting pipes have brought 

 up from the roots, are united. The details of the process are not 

 understood ; possibly they never will be. 



We are now in a position to understand why leaves generally 

 take the form of thin, more or less horizontally expanded, plates. 

 It is that each chlorophyll-bearing cell may receive its due allow- 

 ance of light and air. Hence the cells near the upper surface of 

 the leaf are closely packed, probably because they are nearest the 

 light. The lower cells are loosely packed, and irregular in shape, 

 probably because they have to depend on the light which has 

 filtered through the more fortunate cells above. This economy 

 of space is very characteristic of both plants and animals. It is 

 obvious, too, that the increased surface which results from the 

 shape of the leaf admits of a greater number of stomata and of a 

 corresponding increase in the amount of carbon dioxide supplied 

 to each cell. The one great work of green leaves is the fixation 

 of carbon, and almost every detail of their structure is arranged 

 for the furtherance of this end. Regarded from this point of 

 view, the stem and its branches are to be considered as organs for 

 bearing leaves and spreading them out, so that they shall not 

 interfere with each other's work. The arrangement of the Wall- 

 flower's leaves in spirals around the stem has the same object. 



We have now rapidly sketched the more essential features of 

 the work done by the root, stem, and leaves of a flowering plant. 

 These must be properly realised if the difficulties, the snares, and 

 pitfalls of plant life are to be sympathetically understood. They 

 constitute the daily routine, " the trivial round, the common task" 

 of plants. But plants, like human beings, have their romance. 

 In Spring they deck themselves in gay colours, and hang out 

 placards for the benefit of bees, and of all others whom it may 

 concern. " Here you may get good honey in return for certain 

 services" is the legend on every brightly coloured petal, and the 

 bees are not slow to take the hint. 



