224 PART III. VEGETABLE PHYSIOLOGY. 



he is dependent for his sustenance on already organized matter. 

 He is, in fact, indebted for his very existence to the constructive 

 work of the plant. But this distinction, which separates with 

 apparent sharpness the chlorophyll plant from the ordinary 

 animal, is not universal. Most parasitic and saprophytic plants, 

 being destitute of chlorophyll, are, like the animal, dependent on 

 organic food materials for their existence. Moreover, chloro- 

 phyll plants are not green throughout; a part of the cells contain 

 green coloring matter, but another part, often the larger part of 

 the plant, contain none whatever. These cannot assimilate their 

 own food-materials ; they are dependent for their sustenance on 

 the organic matters elaborated by the green cells. In the way 

 they are nourished they agree essentially with animals, yet their 

 origin is the same as that of the chlorophyll-cells with which 

 they are associated ; both are products of cell-division from 

 the original germ-cell in the embryo-sac. 



Lastly, as regards the modes of reproduction. Here again 

 the parallelism between animals and plants is very complete and 

 striking. Among both are found organisms which reproduce by 

 cell division, in its various modifications of budding, fission and 

 internal cell-formation. Many animals bud and branch like 

 plants, and some of these approach so nearly to plants in ap- 

 pearance and habit of growth that it requires careful observation 

 to distinguish them. The lowest animals, like the lowest plants, 

 reproduce by cell division only ; organisms a little higher in the 

 scale, in each kingdom, reproduce by conjugation or the union 

 of two similar cells ; and the highest animals, as well as the 

 highest plants, reproduce by fertilization, or the union of two 

 different cells. 



Plants and animals, therefore, resemble each other funda- 

 mentally; the protoplasm which constitutes the physical basis 

 of life of both has in both the same essential properties. We 

 must regard plants and animals as two branches of a common 

 trunk. The first living being that made its appearance on our 

 globe was probably neither distinctly plant nor animal, but a bit 

 of undifferentiated protoplasm. From such a form, for a com- 

 mon trunk, have diverged the two great branches of the tree of 

 life, each of which, by countless ages of growth, and repeated 

 branching, has given rise to an innumerable and richly varied 

 series of forms. 



