402 THE BIOLOGY OF FLOWERING PLANTS 



flower swells up and becomes fleshy. In the rose hip the 

 cup-shaped axis of the perigynous flower gives rise to the 

 succulent and showy part of the fruit. 



The peduncle rarely takes part in fruit formation, though 

 it is frequently much strengthened in relation to, and 

 perhaps as the result of, the increased weight it must bear. 

 In Anacardiiim occidentale, the cashew nut, the one-seeded 

 kidney-shaped nut is borne on a heart-shaped, fleshy swelling 

 of the peduncle. In the fig the flowers are borne on the 

 inner surface of an urn-shaped axis, from which the fleshy 

 part of the fruit develops. 



Usually the style withers away after fertilisation, but 

 occasionally it undergoes development on totally new lines, 

 and takes on fresh functions in connection with seed 

 distribution. The styles of Anemone Pulsatilla and of 

 Dryas octopetalla grow into long, feathered organs ; the 

 style of Geum urbanum becomes mechanically strengthened 

 and provided with a hook ; the styles of Geranium and 

 Erodium also become strengthened with mechanical tissues 

 of peculiar hygroscopic qualities. 



The calyx frequently withers ; frequently it persists 

 for longer or shorter periods, sheltering the young fruit. 

 Occasionally it undergoes fresh development, taking on 

 new functions. The pappus of the fruits of the valerians 

 is an outgrowth of the rim which represents the calyx in 

 the flower ; the pappus of the Composites may possibly 

 be homologous with a calyx. In the tropical Anisoptera 

 and Dipterocarpus sepals enlarge enormously and form 

 great wings. In a few cases the sepals swell and form a 

 fleshy envelope, e.g. in Dillenia retusa and Stictocardia 

 tilicefolia. 



In many Compositae the involucre closes in and protects 

 the developing fruits, e.g. in the dandelion. In a few, as in 

 Xanthium and Arctium, it persists as a resistant and hooked 

 envelope serving in distribution. 



Fall of Corolla. — The corolla and stamens take no part 

 in these changes ; they wither and fall off^. Often the 

 individual petal, or the corolla as a whole, falls before 



