X INTRODrCTION. 



plants, there may be much instruction derived, which will be 

 found a valuable contribution to our knowledge of the repro- 

 ductive function in more highly organized beings. 



In the animal organism, the nutritive and reproductive func- 

 tions are greatly complicated by the presence of a nervous 

 system. In plants, these two grand functions of organic life 

 are carried on free from nervous influences, and therefore 

 under greatly simplified conditions. The careful study of 

 these functions, thus simplified in plants, ought therefore to 

 precede the investigation of their higher and more complicated 

 phenomena as manifested in animals. 



It is undeniable that the plant takes precedence of the 

 animal in nature, being elaborated out of inorganic matter as 

 material for the subsistence of the animal. It would therefore 

 seem to be the most natural and philosophical mode of investi- 

 gating the phenomena of life, first of all, to see to what extent 

 its functions have been expressed in plants. 



All organic matter appears to be only a manifestation of life 

 in difierent degrees of development, and a plant may be truly 

 regarded as the simplest manifestation of its functions. 



In the author's " Principles of Botany, as exemplified in the 

 Cryptogamia," it was shown in sections 50, 51, that the sim- 

 plest plant in nature is the plant cell, which " constitutes an 

 entire vegetable without organs, imbibing its food by endosmo- 

 sis through every part of its surface, which it converts into the 

 materials of its own enlargement and growth, and finally into 

 new cells, which constitute its progeny." But as we advance 

 in the scale of organization, the cells thus generated do not 

 separate from the parent plant cell ; on the contrary, they 

 remain united with it, to a greater or less extent, until we find 

 individual plants composed of a mass of such cells, all mutually 



