PREFACE. 



After the fourth edition of my 'Text-Book of Botany' (1874) had nearly 

 passed out of print, I received from the publishers, as well as from botanical friends, 

 repeated invitations to prepare a fifth edition. It is, however, an old experience 

 that while one works up with pleasure a second and even a third edition of a 

 comprehensive work, frequent repetition eventually becomes inconvenient or even 

 painful to the author. Having experienced this sufficiently with the fourth edition, 

 I was unable to make up my mind to a fifth. Apart from other circumstances, 

 I was driven to this to an important extent by the progressive development of 

 my scientific convictions. My mode of comprehending important questions of the 

 Physiology of Plants had undergone changes in various directions, particularly in 

 consequence of my compilation of the 'History of Botany'; like others, more or 

 less subject to the prevailing opinions of the present, I had held as important 

 matters which I was gradually impelled to recognise as insignificant and tran- 

 sitory; higher stand-points and freer prospects opened out to me in the course of 

 time, and the form of my text-book would no longer adapt itself to the advanced 

 view. The artist may touch up his composition here and there with a few 

 strokes of the pencil, or even make greater alterations ; but that is not sufficient 

 when the composition itself has ceased to be the expression of his idea. This is 

 the position in which I find myself with respect to my text-book, since the chief 

 thing in it to me is the composition, the form of the exposition as a whole. 



Moreover for several years past the wish had been taking a more and more 

 definite form in my mind, to set forth the most important results of the physiology of 

 plants in such a manner that not only students, but also wider circles, should be 

 interested in them. That object, however, is only to be attained by a freer form 

 of exposition, and I believe I have found it in the choice of lectures. It is not 

 only the right but also the duty of any one who lectures, however, to place in 

 the foreground his own mode of viewing the matter ; the audience wish to know 

 and should know how the science as a whole shapes itself in the mind of the 

 lecturer, and it is comparatively unimportant whether others think the same or 

 otherwise. 



I would have the present book criticised from this point of view. It is 

 intended to introduce students and cultivated readers generally to the study of 



