LECT. V.] THE ROOT. 193 



left in the soil, it will throw up a new stem, which 

 in its turn produces an extension of the root. But 

 if it be injurious in some instances, it also serves 

 very important purposes in the economy of nature. 

 Thus the sand Reed-Grass, Carex arenaria, by 

 means of its creeping roots, binds together the 

 dry sand of the flats on the sea-shore where it 

 grows ; and assists not only in forming a fertile 

 soil where sterility would otherwise reign ; but 

 by preventing the sand from drifting, preserves 

 from destruction the neighbouring fields, which 

 already repay the labours of the agriculturist. 



We must not, however, confound the creeping 

 with the progressive root (R. progrediens) , which, 

 in extending itself, likewise shoots up stems and 

 herbage at intervals ; since it differs in this cir- 

 cumstance, that as it advances anteriorly it decays 

 posteriorly; thus causing an obvious progression 

 of the plant ; and at the same time limiting in a 

 considerable degree its multiplication. Its direc- 

 tion also is not necessarily horizontal, like that of 

 the creeping root, but may be perpendicular ; the 

 cause of the progression in that case being the 

 production of a new root laterally : and, in this 

 respect, these roots, although the caudexes are not 

 tubers, yet have a close affinity with the attached 

 tuberiferous roots. Thus the root of officinal 

 VOL. i. o 



