THE LOWER FORMS OF LIFE. 



13 



with the interior of the leaf, they constitute the breathing apparatus 

 of plants. These openings or mouths are termed " stomata," and it 

 is through their media that some of the most important operations 

 in the economy of the plant are performed. These stomata are very 

 numerous in the leaves of some plants, such as the lilac, in which 

 160,000 to the square inch have been calculated under microscopic 

 examination. And it may be noted here that in water plants, the 

 leaves of which swim on the water, as the lily, these stomata are in 

 the upper part of the leaf. (See Fig. 6.) 



Now let us go to our friend, Mr. Goadby, and ask him to illustrate 

 for us the structure of a leaf as seen through the microscope. He 

 readily furnishes us with the following microscopic view of a trans- 

 verse slice cut very thin from the leaf of the common garden balsam. 



I have selected the balsam to illustrate the structure of leaves, 

 because it is thick and shows the parts clearly ; but all leaves are 



Fig. 6. 



a> cellg of the upper cuticle or skin _ 

 6, cells containing chlorophylle c c, diges- 

 tive or nutritive cells in central and under 

 part of leaf d, cells of the lower cuticle 

 or skin, containing the stomata, or air 

 openings e, two spiral vessels. 

 Fig. 5. 



Fig. 5 (altered from Goadby). Vertical section of leaf of the common garden balsam (highly 



magnified). 

 Fig. 6 (after Balf our) .Stomata as seen on the upper surface of water plant (Ranunculus 



aquaticus, highly magnified). 



constructed more or less on the same model. They are, in fact, 

 formed of a vast number of photophyta, divided into sets, each set 

 performing a distinct and separate function. Thus we have the top 

 layer, forming the epidermis or skin ; just below the pigment cells ; 

 then the digestive or nutritive cells ; and, lastly, the lower skin and 

 the mouths of the stomata. There are also a series of vessels which 

 are made up of cells and formed into tubes. These tubes are com- 

 monly known as veins, and are well seen in the skeleton leaves we 

 pick up in our garden in winter. In the wheat and allied plants 

 they run parallel to each other. They are called " vascular vessels," 



