'i'HE ANGIOSPERMAE 1521 



combined with a scarlet, orange or white aril, but more often it is the carpels 

 which provide the contrasting colour as, for instance, the scarlet carpels 

 and black seeds of Sterculia, or else the persistent calyx, as in Cleroden- 

 dron fargesii, a well-known garden shrub with blue berries surrounded by a 

 red, fleshy calyx (Fig. 1389). In other species the contrast may be between 

 ripe and unripe fruits, as in Viburnum lantana, whose unripe fruits are 

 scarlet, while the ripe ones, which alone are eaten, are black. Sorbus vilmor- 

 iniana has umbels of fruits, those unripe being red and the ripe ones white. 

 In Mo?nordica charantia, the wild Pumpkin, there are three colours: the 

 fruit which is reddish, the seeds which are black and the arils which are 

 orange. Shades of red are the commonest colours in fruits and they are well 

 adapted to show up clearly against the green foliage. The colour patterns 

 on the seed-coats of some species of Phaseolus, Lat/iyrus and Ricinus do not 

 seem to be attractions to birds, as the seeds are mechanically dispersed, and 

 it has been suggested that they serve rather to conceal the seeds, as they lie 

 on the ground, from the eyes of rodents and other small seed-eating animals. 



External adhesion is brought about by gummy secretions or by hooked 

 hairs or bristles. The latter are much more characteristic of fruits than of 

 seeds and will be described later. Seeds provided with hooked hairs are 

 decidedly rare, almost the only example being in Barclava, a small member 

 of the Nymphaeaceae, which seems to be dispersed by wild pigs in Malaya. 



Carriage of seeds in mud is very common, especially those of marsh or 

 water plants, which are picked up on the feet of wading or running birds, 

 Charles Darwin was the first to investigate this means of dispersal and he 

 raised many plants from specimens of such mud cakes on birds' feet, 

 especially species of Juncus, Carex, Polygonum, and aquatic Gramineae. 

 Small plants like Lemna or portions of Elodea may also be thus transported 

 and they will withstand exposure to the air for long enough to be carried 

 by ducks for long distances. Not only birds, but hooved animals, human 

 boots and cart-wheels may carry seed-bearing mud about with them. Small 

 floating seeds may also be picked up on the feathers of swimming birds. 



Water Dispersal. Dispersal by water includes both fresh water and sea 

 water. The latter has been made the subject of extensive studies, especially 

 by Darwin and by Guppy, because of its importance in the colonization of 

 distant islands. 



Almost any seed that is light enough to be wind-dispersed may also be 

 water-borne and many larger seeds which will float are carried by rivers. 

 The only requirement for long-distance transport is a sufficientlv imper- 

 meable testa to withstand immersion for a not too prolonged journey. 

 Many seeds that are primarily distributed by wind are also capable of 

 floating if they fall into water. Even some seeds which do not float will 

 germinate beneath water, and the seedlings rise to the top and are carried 

 off. Apart altogether from moving bodies of open water, a factor of very 

 widespread influence is rain-wash in the soil. Vast numbers of seeds and 

 fruits are moved thus every year, especially on sloping ground, while others 

 are buried in the soil, where they may long remain dormant, a form of 



