xiv Introduction, 



genus as Eosa or Lilium, and the application of this plan will 

 be clearly seen. Perhaps nothing is more artificial, in a sense, 

 than the so-called natural system of botanists. Scarcely 

 two botanists agree as to what should constitute an order, 

 a genus, or a species. These differences of opinion often 

 appear greater than what they really are, for they all resolve 

 themselves into the question of the value to be attached to 

 certain characters. The cultivation of plants and compari- 

 sons of the same species from different parts of the world, 

 have taught us that variability, more or less rapid or wide 

 according to conditions and circumstances, is a prominent 

 feature of most species under observation. What the limits of 

 this variability are, nobody has yet determined, and some de- 

 clare it to be illimii able. But this is not the place to discuss 

 the stability of species ; suffice it to say that for all practical 

 purposes there is little difficulty. With the horticulturist it 

 becomes a question whether a certain plant, whatever rank we 

 may assign to it, be worthy of cultivation, either for its use or 

 beauty. And this point decided, there is little to prevent him 

 from ascertaining whether it will be better to propagate it 

 direct from seed, or by some non-sexual means, as from cuttings, 

 grafting, etc. Of course the method adopted will depend upon 

 the easiest way of transmitting it pure. 



There are no general rules by which botanists are guided in 

 defining species. In some groups of plants, certain organs 

 appear to be so constant in their form, number, hairiness, etc., 

 as to characterise species, whilst the same set of organs in 

 another group of plants vary so much as to be of no use in 

 distinguishing species, and consequently the botanist has re- 

 course to a different set of organs, affording more permanent 

 and reliable characters. This, coupled with the variation of 

 plants under diverse conditions, will explain the difficulties 

 experienced in determining species from written descriptions. 

 Indeed, it may safely be averred that the most accomplished 

 botanists often fail, after careful study, to identify a plant with 

 its description, even when that description is as perfect as it is 

 possible to make it from half-a-dozen or more specimens ; and 

 it is usually considered necessary to compare the new specimen 

 with the original in the case of little known species. We 



