ENVOI 



As to author's afterthoughts and the more or less sincere 

 apologies that often find place in a preface, I have little to 

 say. Qui s'excuse, s^ accuse. Only one point should be men- 

 tioned that cannot be fairly introduced elsewhere. It is that 

 but little reliance has been placed on abstracts and references 

 at second-hand except as regards some analytical data; most 

 of the sources quoted have been seen in the original by me, 

 though possibly a smaller proportion for the second than for 

 the first edition. 



Another function of a preface is to be the expression of the 

 author's acknowledgments, a sort of grace before meat : often 

 scamped by the reader anxious to get to the meal — though, to 

 be sure, it is the author's grace and not the reader's. I think 

 that the following acknowledgments will be better noted 

 because they come at the end: 



To Dr. George T. Moore, Director of the Missouri 

 Botanical Garden, St. Louis, Missouri, U.S.A., for kind 

 permission to reproduce Fig. i from the "Bulletin" of the 

 Garden. 



To Dr. A. E. Hitchcock, of the Boyce Thompson Institute 

 for Plant Research, Yonkers, New York, U.S.A., for kind 

 permission to reproduce Figs. 2, 3, 4 and 5 from the 

 "Contributions" of the Institute. 



To some senior colleagues of Rothamsted Experimental 

 Station, for having read and criticized portions of the manu- 

 script of the first edition (the blame for any mistakes remain- 

 ing mine, of course), and finally: 



To Dr. H. L. Pearse and the Imperial Bureau of Horticul- 

 ture, both of East Mailing, Kent, for courtesies in connexion 

 with the supply of references. 



136 



