of New York 21 



place. This, is the reason why leaves have been called the 

 laboratory of the trees. The principal product derived from 

 this process, known by the technical name of photo-synthe- 

 sis, is starch. As rapidly as the food is manufactured in the 

 leaves, it makes its way down through the cells of the twigs, 

 branches, and the stem. A continuous stream of nutritious 

 sap is moving downward. The thin layer of cambium cells 

 which encircle the tree then draws upon this food supply to 

 build up new wood, bark, and other tree tissue. When there 

 is an excess of food material it is stored in the roots, stems, 

 branches, and twigs for later use. 



It is interesting to know that in making the starch, oxy- 

 gen is a by-product. This explains why it is healthy to have 

 green growing plants about us in daytime. Leaves prepare 

 food only in daytime, and their output is the greatest in full 

 sunlight, and is almost negligible during dark nights. This 

 is the reason why we find the most luxuriant tree growth 

 in moist, sunny, and warm regions. It is also worth know- 

 ing that during the periods of the year when the leaves are 

 not manufacturing food, the trees live upon a food supply 

 stored up during the long and light days of summer time. 



T 



THE ENEMIES OF TREES 



REES have many enemies. They are fighting for their 

 . lives all the time. There are 200,000 known kinds of 

 insects that attack trees. It is estimated that caterpillars, 

 beetles, borers, and other insects cause a loss of one hundred 

 million dollars every year. Birds help us a lot in holding 

 the insects in check. But they cannot wage war unaided. 

 We must take a hand in this serious insect problem. 



When we think of tree enemies we must not overlook tree 

 diseases, such as blights, rusts, and rots.. They too are a 

 serious menace. These diseases affect the tree's health, just 

 as human diseases affect our health. Not many years ago the 

 chestnut was the foremost tree in many eastern states. Now 

 middle-size to large chestnut trees are very scarce. There is a 

 good reason for this. In 1904 the deadly chestnut blight was 

 imported from China. In twenty years it travelled over 

 practically the entire range of the chestnut, killing trees by 

 the millions. So far no practical method of control has been 

 found. As a result of its destructive work the chestnut tree 

 is rapidly vanishing. 



There are thousands of other tree diseases continuously at 

 work holding back the growth of trees. And decay is always 

 hard at work destroying the wood that the trees have built 

 up. Trees must be kept strong and healthy so they can 



