472 GENERAL MORPHOLOGY OF PLANTS 



the floor and interior occupants, and also room for the boles or 

 tree trunks (called by foresters the wood mass of the forest) which 

 support the canopy and provide the channels for communication 

 and food exchange between the floor and canopy. The canopy 

 manufactures the carbohydrate food and assimilates the mineral 

 and proteid substances absorbed by the roots in the soil; and 

 also gets rid of the surplus water needed for conveying food 

 materials from the floor to the place where they are elaborated. 

 It is the seat where energy is created for work; and also the place 

 for seed production. 



641. Longevity of the forest. The forest is capable of self 

 perpetuation, and except in case of unusual disaster or the action 

 of man, it should live indefinitely. As the old trees die they are 

 gradually replaced by younger ones. So while trees may come 

 and trees may go, the forest goes on forever. 



642. Age of trees. Many trees live for several centuries. A 

 few trees are known which have lived several thousand years. 

 It is said there is in Kent, England, a tree of the genus Taxus, 

 3000 years old; also that there are now living on the slopes of 

 Mount Etna chestnut trees from which Homer might have gathered 

 nuts; in southern Mexico there is an old cypress tree (Taxodium) 

 believed to be about 6000 years old, and in the Cape Verde Islands 

 an Adansonia of similar age. Another account states that this 

 old cypress in Mexico is about 2500 years old. It is difficult to 

 get accurate data concerning trees of such age, but in the case of 

 the big trees of California (Sequoia washingtoniana) data have 

 been obtained by counting the annual rings of a number of trees, 

 which shows their age to range up to 4000 years. 



643. Forests do not materially increase rainfall of a 

 region. In a study of the climatic vegetation regions it is clear 

 that the forest is dependent on rainfall, and below a certain 

 minimum annual precipitation, not very definitely determined, 

 forests will not develop, and of course the rainfall must be rather 

 evenly distributed throughout the year, or at least through the 

 growing season. But that the rainfall of a region is influenced 

 by the forest to any great extent, as is often supposed, is not so 



