DISTRIBUTION OF WEEDS 23 



(7) Plumed Fruits. By far the greatest number of wind- 

 carried weeds are provided with this type of mechanism, and 

 the great majority, if not all, belong to one order of plants, 

 the Compositae. The Compositae, world-wide in distribu- 

 tion and outstanding in number of species and in the 

 multitude of individuals, most probably owe much of their 

 pre-eminence to the fact that they have developed a 

 thoroughly efficient method of distributing their seeds. The 

 plumed fruits vary in size, some being quite tiny while 

 others are comparatively large and heavy, but all agree 

 in having the calyx, or outer floral envelope modified into a 

 number of hairs called the pappus. These hairs radiate 

 from a common centre, sometimes rising directly from the top 

 of the fruit (as in groundsel and coltsfoot), sometimes being 

 raised above the fruit on a slender beak, as in dandelion and 

 goatsbeard. There is great variation in the type of hairs, for 

 in some cases they are short bristles, as in hardhead ; in 

 others they are quite simple but long and silky, as in groundsel ; 

 in others they are feathered, as in creeping thistle, and yet 

 again the hairs may be outstanding and interlacing so as to 

 form a kind of web, as is well seen in goatsbeard. Among the 

 common weeds that possess plumed fruits may be mentioned 

 thistles (Cirsium arvense (Fig. 8 B), C. lanceolatum, Carduus 

 nutans, etc.), cudweeds (Filago germanica and Gnaphalium 

 uliginosum), groundsel (Senecio vulgaris) (Fig. 8 E), sowthistle 

 (Sonchus arvensis and .$. oleraceus], dandelion (Taraxacum 

 vulgar e} (Fig. 8 D), goatsbeard (Tragopogon pratensis) (Fig. 

 8 F), coltsfoot (Tussilago farfara) (Fig. 8 A), hawksbeard 

 (Crepis spp.\ mouse-ear hawk weed (Hieracium pilosella), hawk- 

 bit (Leontodon spp.) (Fig. 8 C). The common hardhead (Cen- 

 taurea nigra) has only short scaly bristles, sometimes mixed 

 with a few longer ones, but the greater knapweed (C. scabiosd) 

 is crowned with a pappus of stiff hairs almost as long as the 

 fruit itself. 



(8) Plumed Seeds. Comparatively few plants are pro- 

 vided with plumed seeds, the only outstanding instances among 

 British weeds being the willow-herbs (Epilobium spp.} (Fig. 9). 

 The fruit is long and narrow and when ripe splits into four 

 pieces which curl back and liberate the numerous small seeds, 

 each of which bears a tuft of hairs. 



(d) Fruits and Seeds Distributed by Animals and Human 

 Beings. Two distinct methods of distribution are included 

 under this heading, in one of which the fruits and seeds attagh 



