30 



BIOLOGY OF PLANTS. 



cies which in any way act upon it, or seem necessary to its de- 

 velo|)tnent in the processes of vegetation, such as soil, food, air, 

 water, gravity, affinity, heat, light, electricity and the agency of 

 man. 



2. " An organized body is one in which all the parts are mu- 

 tually means and ends,"* that is, " each portion ministers to the 

 others, and each depends upon the other," the parts make up the 

 whole, but the existence of the whole is essential to the pre- 

 servation of the parts. The parts are organs, and the ichole is 

 organized.^'' 

 » " We conceive animal life as a vortex, or cycle of moving matter, 

 in which the form of the vortex determines the motions, and 

 these motions again suj)iJort the form of the vortex ; the station- 

 aiy parts circulate the fluids, and the fluids nourish the perma- 

 nent parts."t 



The same view may be taken of plants. In some vegetable 

 products, the organs appear in a distinct form, as in the wood, 

 leaf and blossom. In other products, as starch, gum and sugar, 

 no such marks of organization can be distinguished. All orga- 

 nized bodies are the products of the living principle, whether 

 those now j)0ssessed of life, or those that have been possessed 

 of it, or those which have been derived from living bodies, as 

 alcohol and vinegar. 



3. A plant is an organized and living substance, springing 

 from a seed or germ, which it reproduces. It is composed of 

 an irritaole, elastic matter, called tissxie. Tissue is of two kinds, 

 the cellular analogous to the flesh and soft parts of animals, and 

 the vascular, which is similar to the bones of animals. 



4. All plants are made up of cells or 

 ve^sicks, (Fig. I, a a a,) of different forms, 

 with thin, transijarent walls. When these 

 cells press against each other, small in- 

 tervals are lefl between them which al- 

 so form tubes, called intercellular canals. 

 They are the vessels in which the sap 

 is carried up from the roots to the leaves. 

 When these intervals increase in size, 

 so as to exceed many times the diame- 

 ter of the cells, they are called the pro- 

 per vessels. 



Fiff 



Kant. 



t Whewell. 



