LEAVES 



3363 



LEBANON 



live on others (see PARASITES), or by those, like 

 molds, toadstools and yeast, which live on de- 

 caying organic matter. 



It is frequently said that the leaves are the 

 lungs of plants. This means that leaves, 

 through their stomata (small openings), absorb 

 oxygen and give off carbon dioxide, in the 

 same manner as do animals through their lungs. 

 The amount of oxygen absorbed and of car- 

 bon dioxide given off, however, is very small 

 compared with the amount of each gas passing 

 in the opposite direction during the starch- 

 making process. Furthermore, the interchange 

 of gas in the breathing of plants is not the fun- 

 damental part of that function. What is of 

 importance is the decomposition of complex 

 substances, and the consequent release of en- 

 ergy. This energy the plant uses to carry on 

 its work. A comparison of the breathing 

 process of plants and animals shows that car- 

 bon dioxide, a deadly poison to animals, is 

 essential to the life of plants. Just as animals 

 cannot live without oxygen, o plants would 

 perish without carbon dioxide. Though some 

 oxygen is taken in by the leaves in the process 

 of respiration, it is but a small proportion of 

 the carbon dioxide absorbed by them in starch- 

 making. 



A third function of the leaf is that of tran- 

 spiration, or the giving off of water into the 

 air. By experimenting botanists have discov- 

 ered that surprisingly large amounts of water 

 are given off by various plants through their 

 leaves: 2,250 gallons were transuired in a 

 single summer by a beech tree 110 years old; 

 an oak tree having 700,000 leaves gave off each 

 day about 180 gallons; and during four months 

 of the growing season an acre of cabbages gave 

 off 500,000 gallons. This moisture represents 

 the surplus water of the crude sap which cir- 

 culates through the tissues of the plant. 



In hot, dry weather plants sometimes wilt 

 because they are giving off more water than 

 they are securing from the soil, and the de- 

 vices they use at such times are interesting 

 examples of adaptation to conditions. The 

 leaves of a corn plant, for instance, often roll 

 up into tubes to keep the plant from wilting, 

 for a curled leaf exposes much less surface to 

 evaporation than one whose blade is fully ex- 

 panded. Nurserymen keep the branches of 

 young orchard and shade trees well pruned 

 partly to help maintain a balance of the water 

 supply, for if the leaves are permitted to grow 

 too profusely the trees will lose more moisture 

 than they can absorb through their roots. 



Why the Leaves Fall. In the tropical 

 regions trees usually keep most of their leaves 

 the year round, and this is true also of such 

 northern evergreens as the pines, spruces, etc. 

 But the greater number of the common forest 

 trees that grow in temperate climes pass 

 through the long winter months without their 

 leafy garments. There are two important rea- 

 sons for the fall of the leaf. During the cold 

 season, when the ground is near or at the 

 freezing temperature, the roots of a plant are 

 unable to absorb much soil-water, and if the 

 broad-leaved trees retained their foliage the 

 leaves would give off so much water the trees 

 would dry up and die. Furthermore, in coun- 

 tries where there is heavy snowfall, the 

 branches of the trees would become overbur- 

 dened with snow if the leaves remained on 

 them, and would consequently suffer injury. 



Important changes take place in the cells of 

 the leaf before its work is over, for its valuable 

 food materials are absorbed by the branches 

 and roots to be used again the following spring. 

 Across the base of its petiole a layer of cork 

 cells forms, and at the proper time there is a 

 break at this point. Then the leaf falls to the 

 ground, forming, with thousands of its fellows, 

 a protective blanket for the roots of the tree. 

 Even the dead leaves are useful; the rains 

 dissolve out their mineral contents and these 

 help in the fertilizing of the soil. It is a pretty 

 fancy that the gorgeous colors of the "painted 

 autumn leaves" are the work of the frost, but 

 scientists tell us that the leaf turns red or 

 golden because of the chemical changes that 

 take place in its cells as it is reaching the end 

 of its period of activity. 



In Decorative Art. Leafage is a favorite 

 form of decoration in wood carving, pottery, 

 ornamental sculpture and architecture. The con- 

 ventionalized acanthus leaf (see ACANTHUS) is 

 the characteristic decoration of the Corinthian 

 column, one of the classic forms in Greek and 

 Roman architecture (see COLUMN). The vine, 

 olive, laurel and ivy were other popular leaves 

 used in Greek and Roman ornamentation, and 

 the lotus leaf appears frequently in Egyptian 

 art. B.M.W. 



LEB'ANON, MOUNTAINS OF, a mountain 

 range of Syria extending for 100 miles parallel 

 to the eastern shore of the Mediterranean Sea, 

 on whose slopes in Bible times flourished the 

 famous "cedars of Lebanon" that King Solo- 

 mon used in the building of the Temple (see 

 / Kings, V). So inseparably is the cedar asso- 

 ciated with these mountains that the name 



