PLANT STUDIES 



PART n, THE WORK OF FOLIAGE LEAVES 



The little birds sang as if it were 



The one day of summer in all the year, 



And the very leaves seemed to sing on the trees. 



summer day, 

 a shady tree 

 es- 



In the middle of a hot, 

 when we sit down under 

 to rest and eat our lunch, we feel 

 pecially grateful to nature for provid- 

 ing us with such a cool resting place ; 

 hut, after all, we must not forget that 

 Nature, though willing to share her 

 bounties is first considering her own 

 children. The leaves that protect us 

 from the burning sun have very import- 

 ant work to do for the tree; so import- 

 ant, indeed, that without such work be- 

 ing done, the tree could not live. Before 

 we consider this work in detail, let us 

 examine a single leaf carefully. 



A leaf usually consists of the flat, 

 green, expanse which we call the blade ; 

 of the petiole, or little stem, by which it 

 is attached to the twig or plant ; and very 

 often of two small leaflets, found at the 

 base of the petiole, called stipules. You 

 will notice, as you have often done be- 

 fore, the ribs and veins w^hich trace the 

 leaf. In the lily, these run parallel, 

 while in the maple they form a network 

 over the leaf which is said to be netted 

 veined. These ribs and veins are 

 much woodier than the rest of the blade, 



-Lowell, "The Vision of Sir Launfal." ^ 

 Openings are called stomata; mouths, 

 literally; their work is not fully known, 

 though they are believed to be useful in 

 both transpiration and respiration. At 

 any rate, they permit direct interchange 

 of air and light between the outside at- 

 mosphere and the inner cells of the leaf. 

 This inner layer of the leaf, known as 

 the mesophyll, is made up of cells that 

 contain small green bodies, chlorophyll 

 grains, that give the green color to 

 plants. In the work of food manufac- 

 ture, it has been found that carbon diox- 

 ide is taken up by the cells, the carbon 

 used, and the oxygen given back to the 

 air. For this reason growing plants 

 about us contribute to our good health, 

 since carbon dioxide is a poison rejected 

 by us when we breathe, while we need 

 plenty of oxygen. After the food is 

 made by the leaves, they gradually send 

 it out through the veins to the main 

 branch of the plant, whence it is con- 

 veyed all over the structure. 



A. second work porformed by the 

 leaves is called transpiration ; by which 

 is meant the elimination of the moisture 

 not needed by the plant. One could call 



which is soft and pulpy in nature, and so the process evaporation except that it is 



they give firmness to the leaf. They are 

 composed of hollow, woody, fibres, and 

 not only give support to the leaves, but 

 act as canals to carry the water and min- 

 eral substances which are needed by the 

 leaf in the process of food manufacture. 

 This brings us to the most important 

 work of leaves — food manufacture; for 



controlled by the living organism; m 

 dry countries the moisture is conserved ; 

 on the other hand, where the plant ob- 

 tains a great deal of water, much of it is 

 given of¥. Transpiration is carried on 

 by each part of the plant, but the mairi 

 work is done by the leaves. The truth 

 of the statement that leaves transpire is- 



leaves are the workshop of the plant, and easily tested by placing a glass over a: 



within their cells the raw material gath- 

 ered from the soil and air is made into 

 material that can be assimilated by the 

 plant. If you find a very thick leaf you 

 can strip of¥ from it a thin layer, the 

 epidermis, or outer covering of the leaf. 

 Looked at through a compound micro- 

 scope, there will be disclosed many little 



small growing plant; moisture will soon 

 gather on the sides. If one can note 

 the moisture given off by a small plant, 

 consider the quantity of water lost each 

 day by a forest. One can readily see 

 that there would be sufficient to make 

 an appreciable difference in the climate 

 of the surrounding country. Even a 



openings, each of which is protected by meadow or a strip of lawn, a single tree, 



guard cells which change their shape or a few plants allay the heat and make 



from time to time so as to increase or more habitable the place where they are. 



decrease the size of the opening. These The third work of the leaves is res- 



65 



