182 BOTANY. [CHAP. v. 



the case of weak- stemmed plants, and also as organs of 

 nutrition in insectivorous plants, have already been 

 noticed. 



As a rule, so long as the corolla is polypetalous and 

 regular, and the stamens hypogynous, the latter are 

 numerous and the mode of self-fertilization predomi- 

 nates, whereas when special provision has been made 

 for favouring insect-fertilization, suggested by the irre- 

 gular gamopetalous corolla, the stamens never exceed 

 ten in number, far more frequently five only, and in 

 many instances even fewer, being reduced in the 

 sage, thyme, valerian, etc., to one or two. A marked 

 division of labour is usually present in the two outer- 

 most whorls of the flower, the calyx being green and 

 protective in function, the corolla coloured and attrac- 

 tive. In some cases, however, the calyx is coloured, 

 when it is described as petaloid, as in the Fuchsias 

 (fig. 49) ; in pendulous flowers the calyx is frequently 

 larger than the corolla and petaloid, becoming the most 

 conspicuous attractive whorl, or it is reduced to exceed- 

 ingly small proportions, so as not to interfere with the 

 attractive features of the corolla, as in heaths and the 

 harebell (Campanula, rotundifolia) . In many flowers the 

 corolla is entirely absent, and in such cases the calyx is 

 often brightly coloured, as in the marsh-marigold (Caltha 

 palustris^), wood anemone (Anemone nemorosa) , etc. 



So far the groups considered have been of primary 

 importance, the result of certain characters being con- 

 stant in thousands of species, which, however, differ 

 widely amongst themselves in minor points of detail. 

 The most pronounced of these minor points constitute 

 in turn the characters of so-called Natural Orders. 



