INTRODUCTORY ESSAY. 21 



who is taught that species are definite creations, constant 

 and unchangeable, without being cautioned as to their power 

 of variation within certain limits, finds, when he begins to ob- 

 serve for himself, that he has constant difiiculty in determin- 

 ing their limits, and that abler judges than himself are equally 

 at fault. The more books he consults, the greater are the 

 discrepancies he meets with; if he has recourse to gardens, 

 he there finds species still more sportive ; and if he travels, 

 he meets with a change of form under every climate ; till at 

 last, perplexed and mortified, he gives up the study of specific 

 botany, and becomes a convert to the belief that species are 

 the arbitrary creations of systematists. And such must be 

 the result in the great majority of instances, while each ob- 

 server has to acquire for himself that familiarity with the 

 amount of variation to which organized beings are subject, 

 which alone will render him a sound systematist. For so long 

 as our early education does not teach us this important prin- 

 ciple, so long shall we find beginners refusing to accept the 

 conclusions arrived at by abler botanists. 



Even if we admit the hypothesis that the existence of species 

 as definite creations is inconsistent with facts, it does not ne- 

 cessarily follow that the study of systematic botany is fruitless ; 

 for such a supposition involves the operation of laws which 

 govern the variations of plants, and in accordance with which 

 they remain fixed for a longer or shorter period ; and such 

 laws it becomes the duty of the systematist to develop. The 

 advocates for their agency principally base their belief upon 

 hybridity, and variability induced by climatic influences ; but 

 we shall attempt to show, that all the legitimate conclusions 

 which can be drawn from a study of these phenomena are op- 

 posed to the theory of universal mutability. 



A. On the effects of Hybridization. 

 Recent experiments have led to the following results : — 

 1 . It is a much more difficult operation to produce hybrids, 

 even under every advantage, than is usually supposed. The 



