VITAL CHARACTERISTICS OF PLANTS. 179 



stop for a moment, to notice how strongly the differences 

 between the vegetable and animal kingdoms are marked 

 out, even in the lowest and simplest forms of both. The 

 Protophytes, like the most perfect plants, draw their nutri- 

 ment from the inorganic compounds which are everywhere 

 within their reach, water, carbonic acid, and ammonia ; 

 by decomposing carbonic acid, they give off oxygen ; and 

 they form for themselves the starch and the chlorophyll, 

 the cellulose and the albumen, which they apply to the 

 augmentation of their own substance. On the other hand, 

 even those humblest Protozoa, the Rhizopoda, can only 

 exist (so far as we can see) upon organic materials pre- 

 viously elaborated by other beings : these they receive 

 ' bodily ' into their interior ; and though mouth, stomach, 

 intestine, and anus, all have to be extemporized every 

 time that the animal feeds, yet the digestion which the 

 alimentary particles undergo in its interior, is not less 

 complete than that which is performed by the most elabo- 

 rate apparatus which we anywhere meet with; and the 

 nutrient materials thus obtained seem to be appropriated, 

 without any further conversion, to the augmentation of 

 the substance of the body. Thus, notwithstanding the 

 remarkable analogy which these two orders of beings 

 exhibit, I cannot see that any difficulty need be experi- 

 enced in separating them, when we are acquainted with 

 their mode of nutrition. The Gregarina constitutes no 

 real exception ; for although it imbibes its nutriment 

 through its entire surface, like the Protopkyte, yet that 

 nutriment has been previously digested and prepared for 

 it by the animal whose body it inhabits ; and in the ab- 

 sence of any oral orifice or digestive apparatus of its own, 

 it corresponds with a far higher group of animals, the 

 Cestoid Worms, which live under the same conditions. 

 Some recent observations, it is true, would seem to invali- 

 date this distinction, by showing that certain Ehizopods 

 and Infusoria have their origin in undoubted plants ; but 

 we must be permitted for the present to withhold our 

 assent from conclusions so strange, and to question whether 

 they may not be invalidated by some unsuspected fallacy. 

 It has been well remarked, however, that l there is no limit 

 to the possibilities of Nature;' and I should be the last to 

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