82 FIRST STUDIB? IN PLANT LIFE 



hangs down with its edge to the Hght. Here, too, let 

 us make a guess. AVhen the gum-tree is young, it is 

 often strugghng with other trees and shrubs as to 

 which shall first get up into the free air and light. At 

 this time it needs all the food and light that it can 

 gather, and so throws out many leaves, and each leaf 

 with its face full to the sun. When the tree has 

 succeeded in this fight, and has got away up out of 

 the scrub into the free air, the sun is then too strong 

 for it, and the leaf begins to get narrower, and no 

 longer gives its full face to the light. The leaf is 

 now sickle-shaped ; and you will notice that the longer 

 edge is almost always turned towards the outside, 

 where the leaf gets the motst light and air. That the 

 early leaves are opposite need not surprise us ; for 

 the seed-leaves are always opposite, and we can trace 

 the gradual change from opposite to alternate leaves 

 in many plants. 



11. The first leaves of the blackwood tree. Have 

 you ever noticed the strange difference between the first 

 leaves of a blackwood tree and the later leaves (fig. 58V? 

 At first the leaves are the usual feathery leaflets of 

 the acacia. This feathery-form of acacia-leaf is well 

 known to you in the common wattle and in the silver 

 wattle. But, after the first leaf or two, the leaf-stalk 

 begins to broaden, and then, perhaps, you find a leaf- 

 stalk with no leaf at all on it. The feathery leaflets 

 grow fewer and fewer as we go up, until we rarelv 

 have anything but the flattened leaf-stalks. Here, 

 then, is a tree that has found that a green, broad leaf- 

 stalk can do its work better than a feathery leaf. On 

 many acacias this green flattened leaf-stalk is so like 

 to a gum tree leaf that you may take it at first slight 



