10 PREFACE. 



the beautiful investigationB that Schleiden had just published 

 upon the structure and growth of vegetable cells, came to the 

 conclusion that animal tissue consisted equally of cells, and 

 that whatever may be the character of the tissues, whether 

 they assume the form of muscle, bone, or blood-vessels, all ori- 

 ginate in cells, of which they are but modifications. 



Let it. be remembered that these grand discoveries, which 

 have given such an impulse to animal physiology within the 

 last twenty years, originated in botanical investigations. After 

 such fruits have been reaped, the study of the physiology of 

 plants ought to be encouraged. Where would have been our 

 knowledge of the histology of animals, but for the botanical 

 researches of Mohl, Schleiden, Mirbel and other distinguished 

 physiologists ? Incalculable, then, has been the amount of 

 good which has resulted to animal physiology, from the study 

 of the simple and beautiful organization of plants, and in the 

 face of these facts, there is no excuse for the coldness and ne- 

 glect with which this department of Natural History still con- 

 tinues to be treated. It is not the mere collecting of species, 

 the technical description of their several peculiarities, and 

 their proper classification and arrangement which is here ad- 

 vocated, so much as the study of their vital phenomena and 

 the laws of their development. No extensive acquaintance, 

 either with rare exotics or the choicer native species, is at all 

 necessary for such researches, for these laws may be studied 

 in the commonest weeds growing around our dwellings. 



The views on vegetable respiration in this work are not my 

 own peculiarities f for they were held by Dr. Gilbert Burnett, 

 an eminent English physician and physiologist. I have also 

 been very favorably impressed with the opinions advanced by 



