INTRODUCTION. 13 



to a great length close to the ground, until the final small 

 autumnal arch is produced by means of which the growing 

 point is enabled to bury itself. On the other hand, its ally 

 It. thf/rsoidens forms a lofty arch even when totally without 

 other support than its own strength, and generally takes 

 root as soon as the end arrives at the soil, never running 

 far along the surface. 



The stem is round or has five bluntish angles, between 

 which the faces, although often furrowed, are usually nearly 

 Hat. Sometimes the lower part is round and the upper 

 angular. The colour of the stem, as is well remarked by 

 Arrhenius (p. 9), is variable according to the place where the 

 plant grows. In shade it is green or greenish, in spots 

 where it is fully exposed to the light of the sun it usually 

 becomes more or less red or purple, and often acquires a very 

 dark tint of the latter colour ; but some species seem to have 

 a greater tendency to assume the dark tint than is possessed 

 by others. The prickles are uniform in shape and direction 

 throughout the stem; or the lower ones are straight and 

 slender, but the rest much stronger, and either j^atent (that 

 is, at right angles to the stem) or deflexed or declining (when 

 they are straight, but directed downwards). In some spe- 

 cies they are all of nearly equal size and placed chiefly or 

 wholly upon the angles of the stem ; in others they are very 

 variable in size and scattered over the faces as well as the 

 angles. In the latter case there is usually a very gradual 

 decrease in their size, so that the smallest prickles ai'e not 

 distinguishable from the slender rigid bristles called aciculi. 

 The aciculi again decrease in strength, and each becomes 

 tipped with a gland, when they take the name of setae'. 



^ The term seta is usually applied by botanists to a strong bristle, 

 but English writers upon the genera Bubus, Rosa and Hieracium confine 



2 



