CHEMISTRY IN AGRICULTURE AND PHYSIOLOGY. 289 
of that contrivance by which the function of exhalation is 
carried on, because it requires you should first take a peep 
into the hidden world, which is exposed to us only by the 
microscope ; but I think 3 7 ou can obtain a good general notion 
of it by fancying you can see the skin (epidermis) on both 
sides of the leaf perforated by minute pores. Through these 
invisible pores the steam is exhaled. Imagine these pores to 
be formed by means of a pair of invisible sausage-shaped 
bladders, filled with vegetable juices; these bladders— cells , 
as they are termed —lying side bv side, and attached only at 
the two ends; by pressing the ends toward the middle point, 
the bladders would curve outwards, and thus an opening like 
a slit or pore would be formed between them. W e may con¬ 
sider this description of apparatus (forming the pores) as so 
many flood-gates which can be opened or shut at the command 
of the sun, in order that the steam may be exhaled or retained 
accordingly. 
Now I do not pretend to assert that this is precisely the 
M ay in which the function is carried on by the mechanism I 
have described, because some of my physiological readers 
may have better notions of such structures. Under the 
microscope we may distinctly see these peculiar arrangements, 
by which the pores are closed and opened ; these pores are 
named by botanists stomata , or “ little mouths.” 
The leaves of a plant, whilst they are endowed with life and 
stimulated by light, are enabled to combine thirteen or fourteen 
out of the sixty-one elements into some one or other of the 
peculiar substances found in its juices, and distinguished as 
organic compounds. Plants are mighty chemists, surpassing 
Liebig himself in their power of effecting combinations among 
the elements of material substances. That justly eminent 
chemist, and many a one less than he, can now manufacture 
sugar out of brown paper, and bread out of saw-dust; and 
they can beat all the ablest conjurors of the good old times 
(when alchemy and astrology directed the undoubting faith 
of wondering admirers), by the marvellous extent to which 
they can carry their transmutation. But not one of all the 
chemists whom the world has yet seen has been able to con¬ 
trive how he might combine the elements of “ inorganic” 
matter so as to form out of them a single organic compound. 
(To he continued .) 
