532 MICROSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTES 



prominent attribute of the vegetable. We shall find that the protozoa 

 (or simplest animals) are supported as exclusively either upon 

 other protozoa or upon protophytes, as are the highest animals upon 

 the flesh of other animals or upon the products of the vegetable 

 kingdom ; whilst many protophytes, in common with the highest 

 plants, draw their nourishment from the atmosphere or the water in 

 which they live, and, like them, are distinguished by their power of 

 decomposing carbonic acid (CO 2 ) under the influence of light 

 setting free its oxygen, and combining its carbon with the elements 

 of water to form the carbohydrates (starch, cellulose, &c.), and with 

 those of atmospheric ammonia to form nitrogenous (albuminoid) 

 compounds. And we shall find, moreover, that even such protozoa 

 as have neither stomach nor mouth receive their alimentary matter 

 direct into the very substance of their bodies, in which it under- 

 goes a kind of digestion ; whilst protophytes absorb through their 

 external surface only, and take in no solid particles of any descrip- 

 tion. With regard to motion, which was formerly considered the 

 distinctive attribute of animality, we now know, not merely that 

 many protophytes (perhaps all, at some period or other of their lives) 

 possess a power of spontaneous movement, but also that the instru- 

 ments of motion (when these can be discovered) are of the very same 

 character in the plant as in the animal, being little hair-like fila- 

 ments, termed cilia (from the Latin word cilium, an eyelash), or 

 longer whip-like flagella, by whose rhythmical vibrations the body 

 of which they form part is propelled in definite directions. The 

 peculiar contractility of these organs seems to be an intensification 

 of that of the general protoplasmic substance, of which the}' an- 

 special extensions. 



There are certain plants, however, which resemble animals in 

 their dependence upon organic compounds prepared by other 

 organisms, being themselves unable to effect that fixation of carbon 

 by the decomposition of the CO. 2 of the atmosphere, which is the 

 first stage in their production. Such is the case, &mong phanerogams 

 (flowering plants), with the leafless ' parasites ' which draw their 

 support from the tissues of their * hosts.' And it is the case also, 

 among the lower cryptogams, with the entire group of FUXGI ; 

 which, however, in a large number of cases, depend rather for their 

 nutritive materials upon organic matter in a state of decomposition, 

 many of them having the power of promoting that process by their 

 zymotic (fermentative) action. Among animals, again, there are 

 several in whose tissues are found organic compounds, such as chloro- 

 phyll, starch, and cellulose, which are characteristically vegetable ; 

 but it has not yet been proved that they generate these compounds 

 for themselves by the decomposition of C0 2 . 



The plan of organisation recognisable throughout the vegetable 

 kingdom presents this remarkable feature of uniformity, that the 

 fabric, alike in the highest and most complicated plants and in the 

 lowest and simplest forms of vegetation, consists of nothing else 

 than an aggregation of the bodies termed cells, every one of which 

 (save in the forms that lie near the border-ground between animal 

 and vegetable life) has its little particle of protoplasm enclosed by a 



