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THE POPULAR SCIENCE MONTHLY. 



us examine this little shred with our microscope, using a lens of mod- 

 erate power. This is from the upper side of the leaf (Fig. 4). How 

 delicate the cell- walls, how beautiful the pattern ! Here is Nature's 

 best attempt at uniformity. All these cells serve identically the same 

 purpose, and, so far as we can see, might have been exactly alike. 

 Yet, while there is similarity, no two are just alike. Let us tear off 

 another shred of epidermis, this time from the lower surface of the 



Fig. 4. Epidermis from the Upper Side 

 of a Leaf. 



Fig. 3. Cross-Section of Tradescantia ze- 

 brina, Wandering Jew (highly magnified). 



Fig. 5. Epidermis from the Lower Side 

 of a Leaf. 



leaf. Here (Fig. 5) we have the same arrangement and forms of cells, 

 but more beautiful and varied outlines, and the cells are more inti- 

 mately interlocked. Our magnifying power is greater, and the cells 

 appear larger ; moreover, we have before us a few cells altogether un- 

 like any of their neighbors, little button-hole-like structures. These 

 are the stomata of the leaf, and through these tiny mouths for the 

 stomata are real oj^enings through the epidermis the exchange of 

 gases goes on between the growing plant and the surrounding atmos- 

 phere. 



Let us now pass on a little further in our investigation of these 

 plant-cells and note the contents of some of them. In our examination 



