ANIMALS AND PLANTS. 121 



multiply itself by a gradual constriction and division of its endoplast, such 

 divisions commonly affecting the nucleus also, and by simultaneous growth 

 inwards of the periplast or cell-wall, so as to cut the primitive cell into two 

 cells, each of which may again undergo a like process of subdivision, Fig. 46, 6. 

 Grouped together in specially arranged forms and plans, more or less modified 

 to suit various purposes, and held together by an intermediate cellulose uniting 

 substance, such cells, yet retaining their own independent powers, though 

 co-operating with myriads of others serve to build up even the highest plants, 

 constitute their organs, and perform their various functions, nutritive or re- 

 productive. Or, one such cell, as in the unicellular microscopic Algse, 6, may 

 embrace within its minute sphere of action all the characteristic vegetative 

 processes absorption, elaboration, and respiration, the growth of its own 

 simple structure, and the reproduction, by division of its endoplast and peri- 

 plast, of its own species, thus evincing the close relationship of reproduction 

 with nutrition, and the unity of all the so-called organic or organizing pro- 

 cesses. Unless in the case of the Mycetozoa, it is not certain that any naked 

 protoplasm, or gymnoplasts, exist in the vegetable kingdom. 



Besides containing all the chemical elements found in animals (see p. 86), 

 even fresh-water plants may have a certain quantity of iodine in their compo- 

 sition ; whilst the marine algae contain both iodine and bromine. 



Resemblances between Animals and Plants. Living animals and 

 plants resemble each other in all the particulars which characterize 

 bodies belonging to the organic kingdom of nature. They are both 

 organized, i. #., composed of parts, complex or elementary^ named 

 organs, destined for special uses ; or, in the simplest or lowest forms 

 of both kingdoms, they consist of distinct structures or tissues, mani- 

 festing vital properties, capable of being called forth by appropriate 

 stimuli. In chemical composition they likewise present a general 

 resemblance, though it was formerly supposed that they were specially 

 distinguished in this respect. Animals were known to contain proxi- 

 mate constituents, named quaternary, because supposed to consist of 

 four elements carbon, hydrogen, oxygen, and nitrogen such as albu- 

 men and fibrin ; while plants were said to contain substances of ternary 

 composition only, i. e., consisting of carbon, hydrogen, and oxygen. 

 But plants, as is now well known, also contain albuminoid substances, 

 such as gluten, legumin^ and others, which, indeed, constitute their 

 most essential living parts; whilst the ternary compounds formed within 

 them, viz., woody fibre or cellulose, starch, sugar, and oil, are merely 

 the supporting portion of the vegetable fabric, or deposits in the gen- 

 eral tissues of the plant. Moreover, starch, sugar, and even a pecu- 

 liar form of cellulose, are found in the bodies of animals, the latter 

 in the skin of certain of the Tunicata, starch and sugar, even in 

 the highest animals and in man. As regards their vital properties 

 and functions, animals and plants also resemble each other, especially 

 in reference to the so-called vegetative functions, both nutritive and 

 reproductive. Thus, both are nourished from without, by processes 

 of absorption and interstitial assimilation; in both the functions of 

 secretion, excretion and respiration are observed ; and a form of cir- 

 culation is present in most animals and in some plants. In both the 

 phenomena of growth take place ; in both, existence is of limited 

 duration ; and, in both, the individual springs from a predecessor or 

 parent, and in turn assists in reproducing new individuals or offspring. 



Differences between Animals and Plants. The distinction between 



