viii PREFACE 



Elementary types have been specially treated, all the essentials being marked 

 in heax-y type, so as to make them easy to follow, even for the beginner, 

 while in each general section a statement of elementary points has been 

 included, on which the beginner may concentrate his attention, leaving the 

 fuller treatment for later study. We emphasize this because we do not wish 

 the impression to prevail that a textbook as large as this must necessarily 

 be far beyond the needs or the grasp of the first-year student. No doubt 

 much of it is beyond him, but we believe that the above provisions for his 

 requirements may make it possible to use the book at all stages, with the 

 advantages which may thus be gained from thorough familiarity with one 

 comprehensive source during several years. 



On one important question we feel obliged to state our opinion, the 

 question, namely, of the use of teleological expressions in describing the life- 

 processes of the plant. 



The natural reaction against the crude teleology of the adaptationists 

 has been carried to extravagant lengths, and has become a pedantic insistence 

 on purely mechanistic terminology, which amounts to a sedulous pretence 

 that the plant is not alive. Such fictional concepts have their undoubted 

 uses, so long as we do not forget that they are simply constructional fictions. 

 The living organism is no doubt a physico-chemical mechanism, and it 

 may be to some extent analysed in such terms, but to insist that it can be 

 completely expressed as a test-tube filled with reactant substances is 

 definitely unscientific. It implies the rejection, a priori, of a whole category 

 of phenomena which are not covered by such a theory, but which are just 

 as much facts as are the chemical reactions, and are indeed those very 

 phenomena which give Biology its validity as a separate science. The 

 existence of purpose in our own nature is practically the only phenomenon 

 of which we have immediate perception, and it is highly irrational to exclude 

 it from all the rest of the universe. We need not use it in our accounts of 

 the construction of a living mechanism, but we must use it in considering 

 the operation of the mechanism or the universe becomes meaningless. It 

 may perhaps be an act of presumption to believe that a living organism can 

 ever be fully understood, but we warn the reader that in our efl^orts towards 

 this goal we shall employ the word " function," with all that it implies, 

 when we think it is needed, and we shall do so on principle and not merely 

 to avoid tiresome periphrasis. 



Botany has moved far since 1829, when Loudon wrote that " the Science 

 of Botany consists of two departments : Phytology and Physiology." The 

 botanical scene has changed many times in the intervening century, and it 

 becomes daily more difficult, as our periodicals show us, to say what is 

 Botany and what is not. In order to cover the subject adequately we have 



