INTRODUCTION. 



In the study of Ruhi it is requisite to take into con- 

 sideration the habit of the plant, as well as the form and 

 structure of most of its parts. A want of information in the 

 first of these respects renders it most difficult and often 

 impossible to refer dried specimens to their true species 

 with cei-tainty'. All the fruticose species throw out long 

 leafy shoots directly from their roots which do not produce 

 any flowers during the first year. The Idcei are sometimes 

 exceptions, for their canes (as the gardeners call them) do 

 sometimes flower at the end in the first autumn. The 

 barren stems, as they are usually called, all rise slightly 

 from the ground at the commencement of their growth, but 

 aftel'wards take difl* -rent directions which are characteristic 

 of the several species. They are either (i) suberect, that is, 

 nearly upright throughout the greater part of their length 

 but nodding slightly at their slender tops ; or (ii) erect-arcuate, 

 when they are nearly as erect as in the suberect speci»es, 

 but terminate often in a kind of knot consisting of a number 

 of closely placed leaves and usually numerous prickles, from 

 which in the autumn one or more slender shoots descend 

 dii-ectly to the ground, where they take root. The other 



^ Caulis in multis plantis ita essenciales prsebet difFerentias, ut eo 

 demto, nulla certitude speciei. Linn. Phiios. Bot. § 276, ed. 2, p. 218. 



