HOW TREES GROW 21 



woody threads. The leaf veins connect with 

 larger tubes in the leaf stalk and these in turn 

 are joined to tubes in the branch. 



Second: Filling in the spaces between the 

 network, is a green pulp, which somewhat re- 

 sembles honey comb in arrangement. It is 

 made up of rows of cells. Each cell is a little 

 bag of delicate transparent skin, filled with 

 colorless jelly. This jelly is called protoplasm 

 — "the thing first made" — and looks very much 

 like the white of an egg. We are told that it 

 contains six ingredients : oxygen, hydrogen, car- 

 bon, nitrogen, phosphorus, and sulphur. The 

 proportion varies according to the supplies 

 taken in. 



Third: We note that, though the protoplasm, 

 or cell jelly, is itself clear, it is so full of float- 

 ing specks of vivid green, that these give their 

 color to the whole leaf. These specks are called 

 chlorophyll bodies. Chlorophyll forms only in 

 the direct light of the sun. Baby leaves, just 

 peeping from the bud scales, appear in various 

 colors. They have, as yet, little or no chlor- 

 ophyll. As one authority puts it: "The sun 

 has not yet given them their working outfit. ' ' 



Fourth: Over network and cells stretches a 

 protective transparent leaf skin, or epidermis. 

 The thickness of this skin varies to suit climatic 



