62 



THE STOMATA OF PLANTS. 



the object, and carefully notice the cavity into which the slit is directed. The minute 

 and regular arrangement of the various parts of each stomate, and of all the stomata on 



Fig. 109. View of ordinary stomata, as seen between the veins of the leaf of the LILY, A, or, ZEA 

 MAYS, B, both endogenous plants, and of an exogenous plant at C. 



Their regularity in figure and position, and the uniformly oval outline, will be observed. 



the cuticle, will excite admiration ; and the more so when, on examining a variety of 

 plants, the little organ is found very variously figured. 



The general outline of the stomate is commonly circular or oval ; hut in the flax 

 plant, the Agave Americana (Fig. 61), and a somewhat similar one, the Yucca gloriosa, 

 it is quadrangular. In Marchantia they resemhle funnels, and are composed of several 

 cells arranged in tiers, and forming tubes, which perforate the epidermis, and terminate 

 in the cavity beneath. In the oleander (Nerium Oleander] the cells have disappeared, 

 and the cavity is simply protected by hairs. This may readily be seen, if a portion 

 of the leaf be placed under the microscope, as above directed. The Myrodendron, 

 punctulatum, growing on trees in the antarctic regions, has a remarkable modification 

 of the stomata. Dr. Hooker states that the stomate expands on both sides into a kind 

 of cup a condition which results from the hour-glass construction which is met with at 

 the aperture. 



But whatever may be the figure of the organ it is so uniform in the same species 

 that certain botanists, as Brown, are of opinion that they might be made a basis of clas- 

 sification. This, however, would be very difficult, on account cf their minute size 

 and the necessity for the constant use of the microscope ; and further, from the fact 

 that a few plants present more than one form of stomate. Thus, in the Nepenthes 

 or pitcher plant, there are two forms of stomata, one being semi-transparent and 

 nearly colourless, of an oblong figure, and with pellucid globules within the cells 

 whilst the other is roundish, red, and more opaque, and rests not over a cavity, but 

 upon a gland. 



It is proper to state that certain observers of eminence have denied the accuracy of 

 the above statement, as to the construction of stomata, and have affirmed that they do 

 not lead into a subjacent cavity, and consequently have no opening at the slit. Some 

 German anatomists have affirmed that the supposed opening is simply a thinner 

 translucent portion of the membrane, and that the slit is the thickened border of this 

 space. Brown believed them to be usually imperforate, and to be formed by an opaque 

 and sometimes coloured membrane. Such, however, is not the opinion commonly 

 entertained ; and we may confidently appeal to the investigations of our readers to 

 refute it. 



Stomata are not found upon all plants, the exceptions being such as are submersed 



