CELLULAR ANATOMY OF THE LEAF 2IQ 



weather, strain, light, physiological work of the leaf, should 

 be recalled to them and further illustrated and explained. 

 The tissues should be studied as protective system, starch- 

 making, strengthening, conducting, aeration, etc., to which the 

 names epidermis, parenchyma, sclerenchyma, ducts, sieve 

 tubes, and intercellular spaces may later be added. In the 

 drawings the cells must be represented as complete structures 

 individually, not simply by uniform shading. Students should 

 be led to view the leaf, not as a mass of cells put together, 

 but as a mass of living substance separated into cells, flattened 

 to expose chlorophyll to light, and needing protection against 

 drying up, a strengthening framework, two sets of conducting 

 tubes, exposure of all living cells to oxygen for respiration, etc. 

 Important, too, is the mode of combination of tissues, how 

 they are arranged to interfere as little as possible with one 

 another's function. 



Something of the excretion system may be made out in the 

 fine large crystal cells (cystoliths) in this leaf. 



This work will require at least ten hours from the average 

 student, and should have more. It is worth it. 



Naturally, they should be shown other leaves, and especially 

 the mode of ending of the fibro-vascular bundles in the areas 

 of green tissue, which is perfectly plain to the naked eye in 

 Asarum leaves, and with a lens in Cabbage. Also forms of 

 trichomes, hairs, etc., which belong with the protective system, 

 should be shown. These should be in the structural herbarium. 



The systems of tissues may well be treated as follows : 



Protective epidermis, cork. 

 Starch-making cortex. 

 Strengthening sclerenchyma. 

 Growth cambium and vegetative points. 



