IV PREFACE. 



l>laiitS; and sincC;, in the more highly organized plants, 

 both the structure and the physiological functions of 

 tlie individual cells become subject to greater depend- 

 once upon the other parts of the plant, in proportion 

 as the collective organization of the vegetable is more 

 complex ; moreover, since functions then present them- 

 selves, of which no trace can be found in the lower 

 plants, it became requisite to take account of the plants 

 of higher rank, and of the various organs which these 

 possess. The treatise, therefore, contains, if an imper- 

 fect, still in many respects, a more extensive resttmS of 

 Vegetable Physiology, than might be conjectured from 

 the title. 



Unhappily, the Physiology of Plants is a science 

 which yet lies in its earliest infancy. Few of its dog- 

 mas can be regarded as settled beyond doubt ; at every 

 step we meet with imperfect observations, and con- 

 sequently with the most contradictory views ; thus, 

 for example, opinions are still quite divided regarding 

 the doctrines of the development of the cell, of the 

 origin of the embryo, and of the existence of an im- 

 pregnation in the higher Cryptogams. Both in these 

 and in other cases, the small compass of the present 

 treatise forbids a more extensive detail of the researches 

 upon which the opposing views are founded ; I hope, 

 however, that I have succeeded in making clearly pro- 

 minent, the chief points upon which these contests turn, 

 and thus, in facilitating the formation of a judgment 

 by the reader ; and, I have never neglected to indicate 

 the literature from which furt.her instruction is to be 

 derived. 



TiruiHCxEJs^, Odobor VJlhj 1851, 



