924 



ECOLOGY 



those of the cocklebur {Xanthium, fig. 12 19), burdock {Arctium), beggar- 

 ticks {Bidens, fig. 1220), hound's-tongue {Cynoglossum), sweet cicely 

 {Osmorhiza, fig. 122 1), and bur grass (Cenchrus). These and similar 

 fruits are scattered abundantly by man and by domestic animals, and 

 some plants (as Xanthium) have thus made a rapid in- 

 vasion of all continents. 



An interesting class of fruits from the standpoint of 

 dispersal consists of those which are fleshy and possess a 

 more or less juicy and edible pulp 

 (fig. 1222). Birds and other ani- 

 mals commonly eat such fruits 

 abundantly, often aiding in the 

 scattering of the seeds. Some 

 birds eject the seeds immediately 

 after divesting them of the edible 

 portion of the fruit, but the ma- 

 jority of fruit-eating animals prob- 

 ably swallow the seeds, especially 

 those that are small; even stones 

 as large as those 

 of the cherry are 

 swallowed by ani- 

 mals as small as 

 the raven. In 

 some cases, as in 

 the dove and the 

 domestic fowl, the 

 seeds commonly 

 are destroyed in 

 passing through 

 the alimentary tract. The most useful animals from 

 the standpoint of dispersal are such birds as the 

 robins, thrushes, and blackbirds, which eat fleshy 

 fruits in abundance, swallowing the seeds, and void- 

 ing them without harming them in the alimentary 

 tract. Obviously such birds are likely to carry the seeds to some dis- 

 tance from the parent plant, as would not be the case with those that 

 reject the seeds while eating. 



Fleshy, edible fruits when ripe usually are conspicuous by reason of 



1219 1220 



Figs. 1219-1221. — Fruits with append- 

 ages which become fastened to animals 

 and thus dispersed: 1219, a fruit of the 

 cocklebur (Xanthium\ whose body is cov- 

 ered with stiff recurved prickles; 1220, an 

 achene of the bur marigold {Bidens), 

 crowned with two sharp and stiff teeth or 

 awns (o) which are covered with reflcxed 

 barbs (6); 1221, a mature fruit (schizo- 

 carp) of the sweet cicely {Osmorhiza lon^ 

 gistylis), consisting of two one-seeded car- 

 pels (c) which separate along the inner 

 face, remaining delicately suspended on 

 slender prolongations of the axis, the car- 

 pophore {(/) ; the carpels readily adhere to 

 passing animals by means of the barbs (6). 



Fig. 1222. — An 

 aggregate fleshy 

 fruit of the mul- 

 berry {Morus) ; 

 such fruits are 

 eaten by animals, 

 the seeds passing 

 undigested through 

 the alimentary 

 tract. 



