66 Vegetable Flujswlogtj. 



the microscope. A further peculiarity is, that while in animals 

 it is a jjeneral rule for the organs connected with the support of 

 the individual life, namel}-, those of digestion, respiration, &c., to 

 be situated in the interior of the body — and the more completely 

 so the more complex the apparatus — in plants the organs of 

 absorption, respiration, &c , are turned outwards and displayed 

 on the surface of the body ; so that as regards general organiza- 

 tion, plants have no internal anatomy ; the study of their external 

 forms corresponds to the study of the comparative anatomy of 

 animals. 



The exposure of the vital organs on the outside of the frame 

 in vegetables is in agreement with the peculiarity of their con- 

 dition as regards external objects. Animals endowed with 

 organs of sense and motion can seek their appropriate food and 

 convey it to an internally-situated stomach, by the surface of 

 which, and of the rest of the intestinal canal, the nutritive 

 matter is absorbed. Plants, fixed to the earth, devoid of organs 

 of sense and motion, are provided with organs which in their 

 natural growth make their way into media whence they can 

 obtain food by simple absorption at their surface : as when roots 

 grow into the soil, and leaves expand themselves in the 

 atmosphere. 



It has been noticed above that when we chemically examine 

 fragments of any of the organs thus characterized, we do not find 

 them of homogeneous or uniform constitution, made up of one, 

 even of two proximate principles or compound elements, or of 

 tv/o or more of them chemically combined. We find two or 

 more of these principles co-existent, and their relative amounts 

 varying according to circumstances. The microscope alone can 

 help us here. By its aid we discover that the organs which we 

 perceive and distinguish by ordinary vision are composed of 

 other extremely minute structures, which being, to a certain 

 sense, complete in themselves, but associated for a common pur- 

 pose, may be compared with the large organs, of which they form 

 part, the latter being in like manner associated to constitute the 

 entire body. 



As in chemistry we arrive in our analyses at elements which 

 cannot be further decomposed, so in microscopic anatomy we 

 arrive at certain forms of structure which do not admit of further 

 subdivision or separation without losing their distinctive charac- 

 teristics as constituents of particular kinds of living bodies, and 

 falling into the condition of mere organic substances, distinguish- 

 able only by chemical characters. For example : a potato- 

 tuber, when in its natural state, appears nearly solid, and to the 

 naked eye its internal substance exhibits no very complex con- 



