USE OF THE MICROSCOPE IN BOTANY. 25 



and exhalation are carried on in plants ; they lead 

 into cavities beneath the epidermis. The usual form 

 of the stomata consists of a number of rounded cells, 

 bordering the opening, with a couple of kidney-shaped 

 cells of a large size in the centre ; between these is a 

 narrow slit when the mouth is open, and a raised seam 

 when it is shut. In some plants the stomata do not 

 open on the surface of the leaf, but lie in depressions 

 in it ; these are lined and guarded with a number of 

 hairs, as in the oleander (see Fig. 6). You would do 

 well to make yourself acquainted not only with the 

 function, but the various forms of the stomata. The 

 examination of their structure is easy. Take a leaf 

 or flower of almost any plant, tear a thin slice off its 

 under surface, put it in a glass slide with a drop of 

 water, cover it with thin glass, and use a power of 

 about 200 diameters. Examine the outer surface of 

 the object first ; then you will see the cells and slit 

 of which I spoke. Now examine the other side, and 

 notice the cavity into which the slit is directed. 

 Stomata are usually more abundant on the lower sur- 

 face of leaves ; but in plants whose leaves float on the 

 water they are found only on the upper surface, as In 

 the water-lilies ; in plants whose leaves are always 

 submerged there are no stomata ; in grasses and such 

 plants as grow in an erect form they are found on both 

 surfaces equally distributed. As many as 160,000 of 

 these little mouths have been counted on each square 

 inch of surface on leaves of some plants. In the 

 liverworts, as in Marchqntia polymorpha, the stomata 

 are of very complex structure. These organs are not 

 found in the roots of plants, nor in the ribs of the 

 leaves : and they are absent from fungi, lichens, and 

 sea-weeds. 



The study of hairs, which are so abundant on many 

 plants, will afford you much pleasure and instruction, 



