30 MORPHOLOGY OP THE BOOT. 



latter are as normal as the primary root ; that is, to stems 

 so situated that they can produce them. Most creeping plants 

 emit them freely, usually from the nodes ; and so do most 

 branches, not too old, when bent to the ground and covered 

 with earth, thus securing the requisite moisture and darkness. 

 Separate pieces of young stems (cuttings) can commonly be 

 made to strike root. Upon this faculty of stems to originate 

 roots depends all propagation by division, by laying or layering, 

 by cuttings, &c. It is mainly annuals and common trees that 

 naturally depend on the primary root ; and most of these can be 

 made to produce secondary roots. Even leaves and leaf-stalks 

 of some plants may be made to strike root and be used as 

 cuttings. (77.) 



49. Duration. By differences in respect to this, either the 

 root or the plant, as the case may be, is distinguished into 

 Annual, Biennial, or Perennial, according to whether life is contin- 

 ued for a single year or season, for two, or for a greater number. 

 The difference is not in all cases absolute or even well marked. 



50. Annuals are plants which, springing from the seed, flower 

 and seed the same year or season, and die at or before its close. 

 They produce fibrous roots, either directly from the embryo and 

 succeeding joints of stem (as in Grasses, Fig. 63), or from a 

 persistent primary or tap-root, more or less thickened into a trunk 

 or divided into branches. The products of vegetation in all such 

 herbs are not stored in subterranean or other reservoirs, but are 

 expended directly in new vegetative growth, in the production 

 of blossom, and finally in the maturation of fruit and seed. 

 This completed, the exhausted and not at all replenished indi- 

 vidual perishes. 



51. But some annuals may have their existence prolonged by 

 not allowing them to blossom or seed. Others, with prostrate 

 stem or branches, may from these produce secondar} 7 roots, 

 which, forming new connections with the soil, enable the newer 

 growth to survive when the older parts with the original root 

 have perished. And many herbs, naturally annuals, are continued 

 from year to } r ear through such propagation from the branches, 

 used as layers or cuttings. Moreover, certain plants (such as 

 Ricinus or Castor-oil Plant) , which are perennial or even arbo- 

 rescent in warm climates to which they belong, become annuals 

 in temperate climates, early perishing by autumnal cold. 



52. The annuals of cool climates, where growth completely 

 ceases in winter, germinate in spring, mature, and die in or before 

 autumn. But, in climates with comparatively warm and rainy 

 winter and rainless summer, many germinate in autumn, vegetate 



