INTRODUCTION. XVII 



inquiries, not empirically, but upon fixed principles, into the 

 qualities of the medicinal plants which nature has provided in every 

 region for the alleviation of the maladies peculiar to it. To horti- 

 culturists it is not less important : the propagation or cultivation of 

 one plant is usually applicable to all its kindred ; the habits of one 

 species in an order will often be those of the rest ; many a gardener 

 might have escaped the pain of a poisoned limb, had he been ac- 

 quainted with the laws of affinity ; and, finally, the phenomena of 

 grafting, that curious operation, which is one of the grand features 

 of distinction between the animal and vegetable kingdoms, and the 

 success of which is wh6lly controlled by ties of blood, can only be 

 understood by the student of the Natural System. 



In every kind of arrangement, which has the natural relationship 

 of objects for its basis, there are two principal inconveniences to 

 overcome. The first is, that as objects resemble each other more or 

 less in a multitude of different respects, it is impossible to indicate 

 all their affinities in a lineal arrangement; and yet no other arrange- 

 ment than a lineal one can be practically employed. The conse- 

 quence of this is, that while the orders themselves are really natural, 

 the same title often cannot be applied to the arrangement of them 

 in masses. For example, Cupuliferse and Betulinese are obviously 

 connected by the most intimate relationship, and, as collections of 

 species, each of them is perfectly natural ; yet one of them stands 

 among Apetalous plants, the other among Achlamydeous ones ; hence 

 the two latter groups are artificial. In fact, it appears from what we 

 at present know, that no large combinations of orders are natural 

 which are not founded upon anatomical differences ; thus, Cellulares 

 and Vasculares, Exogense and Endogense, Gymnospermous and 

 Angiospermous Dicotyledons, are natural divisions ; but Apetalae, 

 Polypetalae, Monopetalse, Achiamydese, and all their subordinate sec- 

 tions, are entirely artificial. 



The second inconvenience is, that the characters which vegetables 

 exhibit are of such uncertain and variable degrees of impiortance, 

 that it is often difficult to say what value should be attached to any 

 given modification of structure. As this is a practical question, 

 which requires to be well understood, I shall endeavour to explain 

 in some detail the nature and relative value of those peculiarities 

 of which botanists make use in determining vegetable affinities ; 

 repeating, as a general rule which is not open to exception, that 

 characters which are purely physiological, — that is to say, which 

 depend upon differences of internal anatomical structure, — are of 

 much more value than varieties of form, position, number, and the 

 like, which are mere modifications of external organs. 



It is a maxim of the Linnean school, that the parts of fructifi- 



