86 SYSTEMATICAL BOTANY. 



proceeding from a common centre (the species). In like 

 manner, in studying the mutual relationship of the several 

 parts of the vegetable kingdom, the same form of distribution 

 constantly forces itself upon the mind; genera and orders 

 being found to be apparently the centre of spheres, whose 

 surface is only defined by the points where the last traces of 

 affinity disappear. 



634. But although the mind may conceive such a distribu- 

 tion of organized beings, it is impossible that it should be so 

 presented to the eye, and all attempts at effecting that object 

 have failed. If in describing the surface of a sphere we are 

 compelled to travel in various directions, continually return- 

 ing back to the point from which we started, and if in pre- 

 senting it to the eye at one glance we are compelled to 

 project it upon a plane, the effect of which is to separate 

 to the greatest distance some objects which naturally touch 

 each other, how much more impossible must it be to follow 

 the juxtaposition of matter in treating of the solid contents of 

 a sphere. 



635. The fundamental principle of systematic botany is, that 

 those plants should be stationed in company with each other 

 which have the greatest degree of affinity, and that those 

 should be placed most remotely which have the smallest 

 degree of affinity. 



636. Affinity is an accordance in all essential characters. 



637. From this is distinguished analogy, which is a con- 

 formity in one or two characters only. 



638. What we call the characters of plants are merely the 

 signs by which we judge of affinity, and all the groups into 

 which plants are thrown are in one sense artificial, inasmuch 

 as nature recognises no such groups. 



639. Nevertheless, consisting in all cases of species very 

 closely allied in nature, they are in another sense natural. 



640. But as the classes, subclasses, groups, alliances, natural 

 orders, and genera of botanists have no real existence in 

 nature, it follows that they have no fixed limits, and conse- 

 quently that it is impossible to define them. 



641. They are to be considered as nothing more than the 

 expression of particular tendencies (nixus), on the part of the 



