316 Trees. 



The raphia palm has leaves 50 to 66 feet long and ^6 feet broad, 

 probably the largest leaves known, but even here you see the 

 area shaded is only about 132 feet in diameter, which is not at 

 all remarkable. 



The regular tree type has been obtained by a simple 

 development; by introducing internodes between the leaf bases, 

 and by continuing to modify and alter the shape of the leaves. 

 Thus a single column, as soon as it has lifted itself above the 

 reach of grazing animals, can rapidly push out branches 

 horizontally, and form a dense crown of foliage. Thus, once 

 it has got a base for development, it can utilise its long standing 

 in the fullest way possible. 



Such a tree may be compared to an empire of living indi- 

 viduals. Not only so, but the life works of these individuals 

 are as different as possible. I am on holiday just now, and 

 I am not going to give a botanical lecture, but I should like 

 for a moment to show how wonderfully the different offices are 

 filled. The living units, the small cell with its protoplasm, are 

 in their youth almost alike. Yet, as they develop and specialise, 

 each takes its characteristic shape as it gets into its own particular 

 line of work. The outside ones become cork, others in the bark 

 produce the tannin, of which 4 per cent, is enough to prevent 

 the growth of fungi. Thus the rabbit and the roe deer are 

 kept off. Through an oak tree during five months of summer 

 a current of water is always passing, entering by the roots and 

 passing off by the leaves. About 250,000 lbs. weight 

 of water passes through it in five months. The cells 

 which absorb this water, the cells in the woody trunk, and the 

 leaves show the most extraordinary finish in their adaptation to 

 it. The pressure inside some of these cells is probably 200 

 lbs. to the square inch. Then again, the leaves regularly manu- 

 facture the sugar and other material. An oak leaf will have 

 some 2,000,000 pores or stomata through which the carbonic acid 

 hurries in. For every i -500th of a pound of wood substance 

 1,000,000 litres of air has been freed of CO2. 



The sunlight falling on the tree is absorbed by the little 

 green chlorophyll bodies in the leaf. In the trunk there are the 

 wonderful storage arrangements by which sugars, fats, oils, 

 everything made by the leaves, is retained within the stem for 

 next year's buds. 



