About Green Leaves 195 



The palisade tissue on the upper side of the 

 leaf contains many cells, and in them all plenty 

 of green chlorophyll bodies. But on the under side 

 of the leaf the cells are fewer and farther apart, 

 and where there are not so many cells there is, of 

 course, less chlorophyll. This is one reason why 

 the under surfaces of leaves are often pale. 



Chlorophyll is formed only In the sunlight. 

 Tender young leaves which have been shut up 

 under bud-scales In the dark have as yet very few 

 of the useful little grains. 



Budding foliage is seldom really green. But 

 as soon as the leaves come out into the sunshine 

 chlorophyll bodies form within the cells in count- 

 less numbers, and their intense color soon over- 

 powers the tints of early spring. 



Over the whole leaf, veins, cells and all, there 

 is a very delicate transparent skin. This is a sheet 

 of oddly-shaped cells, fitting into one another, 

 with tongues and curves, like the pieces of a puz- 

 zle. Generally these contain no chlorophyll, so 

 that the leaf skin, or " epidermis," Is transparent. 



Some leaves borne by tropical plants are pro- 

 tected by a very thick skin — but for this the fierce 

 sunshine would dry all the juices out of the foli- 

 age. The India rubber tree, a native of the East 

 Indies, has leaf skin composed of three layers of 

 cells. 



The green color in a living leaf is a lure to 

 catch the sunbeams, and when they are caught they 



