FLORAL FORMS AND THEIR RELATIONS TO INSECTS 311 



FIG. 417. WINTER CHERRY 



(Physalis), 

 Showing the accrescent calyx. 



Notice how the corolla of the White Cam- 

 pion is constricted near its upper end by the 

 toothed or dentate calyx. This is another con- 

 trivance for shutting out unwelcome visitors. 

 Only a thin proboscis, at least three-fifths of an 

 inch long (such, for instance, as that of the Small 

 Elephant Hawk-moth (Chcerocampa porcellus], 

 which often visits and cross-pollinates the flower), 

 could reach to the fleshy part of the ovary where 

 the honey is stored. In fact, both the calyx- 

 tube and the elongated claws of the petals assist 

 in preserving the nectar for those insects whose 

 visits are really serviceable to the plant. In 

 flowers with salver-shaped (kypocrateriform) 

 corollas, like the Primrose and Common Lilac 

 (Syringa vulgaris), the tubes formed by the 

 cohering petals answer much the same purpose as the clawed bases of 

 caryophyllaceous corollas, and also protect the pollen from drops of rain 

 and dew the latter an important consideration in the case of plants 

 which dwell amid mountain-mists, like the delicate species of Primulacese 

 belonging to the genus Androsace, and many species of Phlox (fig. 421). 

 "If flowers of Aretia glacialis, a plant growing on the moraines of glaciers, 

 are examined after a shower," says Kerner, " it is found that every one has 

 a drop resting upon it which slightly compresses 

 the air in the narrow tube of the corolla, but 

 cannot reach the pollen upon the anthers lower 

 down the tube. A subsequent shake or puff of 

 wind causes the drops to roll off the limb of the 

 corolla, or else they are got rid of by evapora- 

 tion ; in either case, the flower becomes once more 

 accessible to insects." Salver-shaped corollas 

 must be distinguished from rotate or wheel- 

 shaped corollas, such as we get, for instance, 

 in purple-flowered Woody Nightshade (Solanum 

 dulcamara). In the former the tubes are long 

 and narrow, in the latter they are short ; but in 

 both the limb is placed at right angles to the tube. 



We come now to the tubular corolla. From 

 what has been said about the uses of caryophyl- 

 laceous and salver-shaped corollas, the purpose of 

 this third form may be readily divined. It, also, 

 has reference to insect-pollination. The Com- 

 mon Honeysuckle (Lonicera peryclymenum) may 

 serve as an example. The sweet-scented flowers 



FIG. 418. GREAT VALERIAN 

 ( Valeriana officinalis). 



Showing the gibbous corolla. 



