CHAP, v.] RELATIONSHIP AMONGST PLANTS. 186 



hand, as a rule, substitutes simplicity of mechanism 

 combined with accuracy of detail in place of what may 

 comparatively be termed a " rule-of-thurnb" arrange- 

 ment ; this idea is illustrated in both vegetative and 

 reproductive parts ; it is only necessary to mention com- 

 pound, sensitive leaves, and the various contrivances for 

 insect-fertilization as compared with antiquated leaves 

 and flowers. The extension of modern groups is illus- 

 trated by the subordinate position occupied at the 

 present day by cryptogams, once the only group in exis- 

 tence, and in like manner gymnosperms, the oldest of 

 the phanerogamic series, that were in turn monarchs of 

 the plant world, have yielded in numbers and position 

 to angiosperms, which at the present day take the lead, 

 due more especially to the scrupulous exactness with 

 which the law of " Division of Labour" is carried out. 



The large divisions of phanerogams are in turn 

 broken up into so-called Natural Orders, characterized 

 by minor points of agreement ; and again, Orders are 

 divided into still smaller groups known as Genera, and 

 finally the different kinds or species constituting a genus 

 are distinguished from each other by less important or 

 what may be termed local characteristics. As to the 

 peculiarities of structure and otherwise that constitute a 

 species, there is a wide difference of opinion, but the 

 following gives an idea as to the scientific conception of a 

 species, that is, all those plants that at the present day so 

 resemble each other in structure and function as to 

 justify the idea that they have originated from a single 

 ancestor. 



