GENERAL INTRODUCTION. 



THERE are two kingdoms, an Animal and a Vegetable, to one of 

 which everything that lives may be assigned with more or less certainty. 

 The contrast between the higher or multicellular animals and plants is 

 too great and constant both in an anatomical and physiological sense 

 to leave room for doubt An animal possesses the power of locomotion ; 

 it has a compact form, a special digestive organ for the reception of 

 solid food, and it is unable to utilise Carbon dioxide as a source of carbon 

 for the production of carbohydrates ; it has organs of special sense with a 

 nervous system, specialised contractile cells or muscular tissue, complex 

 excretory products, and in the majority special organs of excretion, lymph 

 or blood, with circulatory organs, &c. Its tissue cells, with few excep- 

 tions, are not isolated or all but isolated by closed and firm cell-envelopes. 

 Supposing that it is fixed, its other characteristics remain ; if it takes on 

 a branched or plant-like mode of growth, examination shows that it con- 

 sists of a connected multitude of typical animals, each one perfect in itself. 

 A few instances are known in which chlorophyl bodies are present ; and 

 it appears probable that they enable the organism to utilise Carbon 

 dioxide for the preparation of starch under the influence of light. Whether, 

 however, the chlorophyl bodies are in all these instances intrinsic parts of 

 the organism is a matter of dispute (pp. 242-5). A typical multicellular 

 plant, on the other hand, is either branched, and it then consists of a root 

 with a stem, bearing a number of repeated organs, the leaves, which are 

 subject to modification, or it is compact and its cells very similar one to 

 another. It is fixed ; it has chlorophyl bodies, which under the influence 

 of light enable it to utilise Carbon dioxide as a source of carbon ; it is 

 able to build up protoplasm and therefore derive tissue elements from 

 the Carbon dioxide of the air, ammonia, nitrates and mineral con- 

 stituents of the soil ; it is devoid of digestive organs, of special sense 

 organs, nervous system, excretory organs, special contractile tissue. Its 

 tissue cells become isolated completely or all but completely by closed 

 and firm cell-envelopes. It may require for food partly elaborated 

 material or fairly complex organic compounds in solution, and may then 



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