THE ANGIOSPERMAE 1545 



Calendula the disc fruits are strongly curved and the convex side is edged 

 with small knobs, while the ray fruits are much larger and expanded into 

 a pair of fringed wings, besides having a dorsal row of spiny processes. In 

 Dimorphotheca the ray fruits are practically straight, tapered downwards 

 and slightly roughened. The disc fruits are broad and flattened, w'ith 

 wing-like expansions, and are smooth (see Fig. 1 182). They germinate 

 quicker than do the ray fruits. A common British plant, Leontodon leysseri 

 {L. hirtus), has a still more marked difference between the fruits of the disc- 

 and the ray-florets, the former being thickest at the top, with a pappus of 

 small scales, and the latter tapering to the top and having a large, plumed 

 pappus. 



All these cases indicate a different dispersal for the two types of fruit, 

 since the winged or flattened fruits are certainly more easily transported 

 by wind than the others, though whether a double dispersal, near and far, 

 is a biological advantage to the plants requires proof. There are many 

 other Compositae with similarly heterocarpous fruits in which there is no 

 difference in their possibilities of dispersal, as in Ridens radiatiis, where 

 both disc and ray fruits have clinging hooks for animal dispersal, though 

 the former are nearly twice the length of the latter. 



Dimorphic fruits (cypselas) also occur in Xanthiiim, the Cocklebur, a 

 genus of Compositae. There are two fruits in each involucre. The upper- 

 most is the smaller of the two and is convex outwards, the lower fruit is 

 convex inwards. The latter germinates in the first season, the smaller 

 fruit does not germinate until the second or a subsequent season. 



Atriplex hortensis (Chenopodiaceae) is often grown as a vegetable. 

 There are two, sometimes three forms of fruit, one which is vertically 

 flattened and held between two large, thin bracts, the fruit being sometimes 

 yellow and sometimes brown. The other is black, is horizontally flattened 

 and has no bracts, but has adherent remains of the perianth, the latter 

 being absent from the fruits enclosed between bracts. At first sight it 

 would be supposed that the bracts are agents of wind dispersal, but this 

 may not be so, for these fruits remain adherent to the plant, while the 

 black fruits are readily shed. If there may be no difference in dispersal 

 here, there is also none discernible in Valerianella, where the terminal fruit 

 of the cyme is several times as large as the lateral fruits, though otherwise 

 similar, or in Polygonum, in which several species produce both three- 

 angled and two-angled fruits indiscriminatelv, which are otherwise identi- 

 cal. 



Under the name of heteromericarpy are included certain cases, parti- 

 cularly in the Umbelliferae, where one part of a fruit differs from the rest. 

 The outermost flowers in the umbels are often markedly exotrophic, that 

 is, they are better developed on the outer side than on the inner side, and 

 the same holds good for the fruits. In Tor His nodosa the outer mericarps 

 of the outer flowers are larger and are furnished with hooked trichomes, 

 which are effective in animal dispersal. On the inwardly directed mericarp 

 the trichomes are small and not hooked, while on the fruits of the inner 



