24 



DICOTYLEDONS 



Fig. 2 1. — Transverse sec- 

 tion of the stem of the 

 Mango tree. 



Under the cork layer is the inner bark, called bast, and inside 

 this are concentric layers of wood. The younger or outer 



layers of wood are that part of the stem 

 through which the sap ascends from the 

 roots to the branches. Any injury to the 

 bark or sapwood may interfere seriously 

 with the circulation of the sap or let 

 disease-fungi enter into the stem. A tree, 

 however, has the power of healing its 

 wounds by a rapid growth of cork at the 

 edges which gradually cover the damaged 

 area. This function is made use of in the 

 process of grafting mangoes. 

 A small Mango plant, about as thick as one's linger, is grown 

 from a seed in a pot, and when it is required to make a graft, 

 a slice is taken out of one side of the stem down as deep as 

 the pith and about an inch long. A branch of one of the good 

 edible kinds of Mango of the same thickness is treated in the same 

 w^ay. This branch and the plant are so placed together that the 

 one cut surface exactly fits the other. They are then tied firmly 

 together with some soft twine and covered over w^ith cowdung. 

 In a short time (a month to six weeks) the two cut surfaces unite, 

 when the branch may be cut away altogether from the tree and 

 the top from the seedling, and the graft Mango can be taken away 

 and planted. 



2. The Leaves are long and narrow, {a) They are so placed 

 on the stem as to allow each to get its share of light: the result 

 is that the Mango tree gives a very dense shade. 



[b) The petioles (leaf-stalks), besides placing the leaves in 

 such a position that they can get light, also save them from being 

 torn wdien the wind blows very strongly, as they are springy. If 

 the leaves were fixed on more rigidly, the branches of the tree 

 would get broken. As it is, the leaf sways from side to side and 

 so escapes most of the wind-pressure. In a similar way, by 

 bending down, they allow any rain-drops falling on them to drop 

 to the ground from their tapering ends, instead of adding to the 

 weight the branches have to ])ear. The leaf must, however. 



