4 INTRODUCTION. 



the organism of the whole earth ; and fourthly, the relation 

 of the human race to the vegetable world. But since 

 each of these four relations is fulfilled by the plant at one 

 and the same time, it is infinitely difficult, if not impossible, 

 to keep each aspect clear and unmixed, and when we enter 

 upon one of these relations with the desire to subject it to 

 closer investigation, we are always involuntarily constrained, 

 sooner or later, to direct our attention to the rest and to 

 draw them within the circle of our researches. Though 

 we establish upon these questions, according to their order, 

 the following branches of study: Theoretical, or Pure 

 Botany ; Systematic Botany ; Geographical and Applied 

 Botany ; yet not one of these can be treated from its own 

 principal point of view alone, if it would lay claim to a 

 scientific or profound character ; still more difficult is it, 

 however, to keep strictly within the boundaries of these 

 four divisions when the object in view is not dry scientific 

 teaching, but a lively demonstration of the more important 

 points. In the following essays, therefore, the division 

 into these four branches can only be adopted to a limited 

 extent, and a freer treatment becomes necessary from the 

 abundance of material which continually allures us to 

 turn aside from our path, to gather here and there a bright 

 or fragrant flower ; or the companionship in which we 

 wander through the land of science, induces us oftentimes 

 to leave the straight, but dusty and fatiguing high-road, 

 now to pursue our course through lanes which wind 

 among pleasant meadows, now to explore a shady forest 

 path. Let us see whither we are going. 



A plant is not, like a crystal or a pure fluid, a perfectly 

 homogeneous body, to fathom the nature of which it 

 suffices to know the substance composing it and its 

 external form, it is far more than this ; built up of many 



