194 Our Field and Forest Trees 



Fig. 49. Portion o£ a white lily 

 leaf cut through and magnified show- 

 ing a section of the thickness, the 

 difference between the upper and 

 lower tissue, and the breathing pores. 



sizes, and they lie loosely together like the stones 

 in the rough walls which border New England 

 lanes. Among these cells are a number of gaps 

 and chinks — " air spaces." 



Each separate leaf-cell is a little bag of delicate 



transparent skin, filled 

 with colorless jelly. 

 This jelly has been 

 named " protoplasm," 

 which means " the 

 first thing molded." 

 Every living creature, 

 vegetable or animal, 

 is largely built up of 

 protoplasm. Chemists 

 tell us that it is made up of six substances, and 

 three of these six are gases. But In the living 

 jelly which fills the cells of summer leaves, the 

 proportion of these six substances varies, almost 

 from moment to moment as work and growth 

 go on. 



The protoplasm in the cell is the important 

 part. The wall around it Is merely to give 

 strength and support. To a student of nature, 

 the jelly-like mass of protoplasm is the " cell." 



Though the protoplasm In the leaf-cells Is clear 

 and colorless, it is full of floating specks of green, 

 so many and so vivid that they give their tint to the 

 whole leaf. These are " chlorophyll bodies," and 

 they cause the green of summer fields and woods. 



