xiv.] BOTANY. 65 



purpose of fertilization. Of these irregular forms the 

 most common monopetalous one is the mask-like or 

 personate (snap-dragon, dead-nettle, Fig. 30); and the 

 most common polypetalous one is the butterfly-shaped 

 or papilionaceous (clover, pea, Fig. 27). The latter 

 is so characteristic of a very large family of plants 

 (pea family) that names have been given to its five 

 petals ; the upper being called the standard, the two 

 side ones wings, and two within them, which are 

 often combined by their lower margins, form the keel. 

 If the visits of bees to irregular flowers are watched, 

 it will be seen, in very many cases, that the form 

 of the corolla is singularly adapted to facilitate the 

 insect entering it in order to obtain honey for itself, 

 when it also carries away pollen from the stamens 

 (Par. 123). 



96. The commonest regular monopetalous corollas 

 are the bell-shaped (campanula), funnel-shaped (con- 

 volvulus), salver-shaped (primrose), and wheel-shaped 

 (pimpernel) . In these, as in the regular polypetalous 

 corollas (apple, Fig. 32, buttercup, Fig. 22), there is 

 little or no relation between the form of the flowers 

 and those of the insects that visit them. In some 

 instances however of regular monopetalous flowers,, 

 there is a special adaptation of the organs of the 

 flower to those of the insect, as where the corolla has 

 a long tube and the insect a long proboscis ; the bee 

 and primrose is an example (Par. 122). 



97. Petals are formed of a thin plate of cellular tissue 

 traversed by vascular bundles (Par. 9). Their colour- 

 ing follows certain rules. The corollas of few or no 

 plants present all the primary colours, and white alone 

 is found in all families of plants with coloured corollas. 



