8 THE DATE PALM. 



open ; also the matrix of soft tissue in the sheath wall soon 

 decays, and only the network of tough fibres is left. With the 

 further growth of the plant the sheath is still further stretched 

 so that even when the stem has attained its maximum thickness 

 the fibres pass a considerable distance round it. 



The cylindrical young leaf-sheaths bind the very young 

 leaves firmly in a perpendicular position on the tree-top, but as 

 their age increases the stretching and splitting of the sheaths 

 allow the leaves to assume positions more and more near the 

 horizontal till withering up they become reflexed downwards 

 on the stem, or are pruned off (see illustration No. 29, page 86a). 

 Thus the youngest and most tender of the leaves are most crowded 

 together and protected by older ones, while the older they become 

 the wider apart they spread, the less they overshadow each other, 

 and the more they can make use of the energy of the sunlight 

 for their work of elaboration of food for the plant. When the 

 leaves have withered, the sheath fibres belonging to them are 

 still strong and are used by the people for various purposes (see 

 page 119, para. 89). 



The central or main axis of the leaf, besides having an internal 

 structure of the same general principle as that of the stem, has 

 a shape admirably fitted to make the best use of its strength in 

 the , directions most required. 



,.^. ; On the main axis below the level of the leaflets are a number 

 of long, sharp thorns (see illustration No. 8, page 6c) which 

 would assist in protecting the tender young terminal bud from 

 damage by the larger animals. In the wild state of the palm 

 the flowers and developing fruits would also be protected by 

 these thorns from some animals. 



The blades of the leaflets are rather thick, and sections of 

 one of them under a microscope show a large number of tough 

 sclerenchymatous bands of tissue running lengthwise in them 

 which make it impossible for winds to break these leaflets across 

 (see illustration No. 10, opposite). The margins of each leaflet 

 are specially strengthened with tough bands of tissue of this sort, 



