410 GENERA AND OEDBRS. 



thamnus Chameecistus and Phyllodooe oaerulea, to whicli the name of 

 Bryanthus erectus has been erroneously given. These hybrids are pro- 

 pagated chiefly by layering and grafting. Cultivators sometimes 

 mark these named hybrids with a cross (X), to indicate their 

 nature. 



Genera. — Certain species are more nearly allied than others, and 

 are conveniently grouped together so as to form a distinct hind or genus. 

 A genus, then, is an assemblage of nearly related species, agreeing 'with 

 one another in general structure and appearance more closely than 

 they accord with any other species. Thus, the various species of Roses 

 compose one genus, which is distinguished by marked characters — 

 more especially by the fruit. Occasionally a suh-genus is formed by 

 grouping certain species, which agree more nearly with each other in 

 some important particulars than the other species of the genus. The 

 characters of the genera are taken exclusively from the parts of fruc- 

 tification, while aU parts of the plant furnish specific characters. In 

 designating a plant the name of the genus is given as well as that of the 

 species. The latter was called by Linnaeus the trivial name. -Thus, a 

 particular species of Rose is called Rosa spinosissima ; the first being the 

 genus, and the second the specific or trivial name. As regards the 

 definition of genera and species, and the binomial nomenclature, no 

 one has conferred so much benefit on science as the great Linnseus. 

 This may be considered as among his highest titles to fame. 



The division of a genus may be illustrated from Hooker's Student's 

 Flora of the British Islands, as follows : — 



Genus — Thalioteum of Linnseus, Meadow-rue, 

 includes the following British species, sub-species, and varieties ; — 



1. Thalictrum alpinum of Linnasus. 



2. Thalictrum minus of Linnaeus. 



Sub-species minus (proper). 

 Variety 1. maritimum. 



,, 2. montanum, a species of Wallroth. 



Synonym. T. calcareum of Jordan. 

 Sub-species, majus of Jacquin. 



Synonym. T. flexuosum of Bernhardi. 

 Sub-species, Kochii, a species of Fries. 

 Sub-species, saxatile, a species of Schleicher. 



3. Thalictrum flavum of Linnseus. 



Variety 1. sphserocarpum of Boswell Syme. 

 ,, 2. riparium, a species of Jordan. 

 ,, 3. Morisonia, a species of Gmelta. 



Orders. — Several genera agreeing in more general characters, 

 although diifering in their special conformation, are grouped together 

 so as to form an order or family. As genera include allied species, so 

 orders embrace allied genera. Subdivisions are also made to facilitate 



