FLORAL FORMS AND THEIR RELATIONS TO INSECTS 337 



FIG. 410. NASTURTIUM. 



Section through flower, showing interior of calyx 

 spur. 



communis), Apple (Pyrus mains), Goose- 

 berry (Ribes grossularia), Strawberry 

 (Fragaria vescci), and Melon (Gucurbita). 

 In other flowers, however the Butter- 

 cup (Ranunculus) will serve as an ex- 

 ample the calyx is deciduous, that is to 

 say, it falls off before the fruit ripens ; 

 while in a few cases, as the Poppy 

 (Papaver), Eschscholtzia, and those inter- 

 esting Malayan shrubs, the Pternandras 

 (fig. 413), where its chief purpose appears 

 to be to protect the young and insecurely 

 fastened petals of the bud, it drops off 

 as soon as the flower opens. Such a 

 calyx is said to be caducous. Some per- 

 sistent calyxes are accrescent that is, 

 they continue to grow after the flower- 

 ing time, like that of the "Winter Cherry 



(Physalis alkekengi), a solanaceous plant often cultivated in gardens. The 



highly coloured inflated calyx of this plant is, indeed, its sole attraction, 



for the cohering sepals so enclose the other organs of the flower as to 



hide them completely from view 



(fig. 417). 



We mentioned the Strawberry 



just now, and we may add that the 



calyx consists (apparently) of a 



double whorl of sepals in other 



words, of two calyxes * and some 



botanists distinguish them by call- 

 ing the outer whorl the epi-calyx. 



Whatever may be the general pur- 

 pose of an epi-calyx, it certainly 



renders good service in the case 



of the Strawberry by protecting 



the young "fruit" from the 



depredations of insects not of 



winged insects, of course, but 



of those which approach the 



coveted object by way of the 



stalk. 



* Another opinion is that there is only 

 one whorl of sepals, the outer structures 

 being regarded merely as stipular growths 

 thereupon. 

 II 4 



FIG. 411. NASTURTIUM (Tropceolum majus), 



With spurred calyx. 



