DISPERSAL BY ANIMALS. 869 



promote their becoming attached to animals. Although the adhesive materials 

 mentioned in vol. i. on p. 615 as exuding from the fruits and seeds of various Com- 

 posites, Crucifers, Labiates, and Polygonacese when they are wetted may be primarily 

 devoted to fixing those structures to a substratum where they can germinate, they 

 also frequently serve a second purpose in sticking them to passing animals. The 

 best instance of this is afforded by the Meadow Saffron {Colchioum), whose seeds 

 stick to the feet of cows, sheep, and horses by means of a comparatively large 

 caruncle, which becomes viscid when it is wetted ; in this manner the seeds are con- 

 veyed from one pasture to another. There is also an instance that has come under 

 my own observation of a small owl (Athene noctua), which, in catching mice, brushed 

 against Wormwood bushes {Artemisia), and when it flew away was all besmeared 

 with the fruits, which had been rendered sticky by a previous shower of rain. The 

 succulent berries of Bryonia, Lycium, Solanum, and various other Cucurbitaceae 

 and Solanacese burst on the slightest touch when they are over-ripe, and sometimes 

 their seeds stick to the hairs and bristles of passing animals, and it seems not impro- 

 bable, from the reports of travellers, that the fleshy Rafllesias, which are found 

 principally on the routes frequented by large pachyderms, are disseminated in the 

 same manner. The mode of dispersion of the seeds of Nuphar and Nyraphcea is 

 also very curious. Their dissemination by aqueous currents has been already dealt 

 with on p. 848, but they are besides conveyed from pond to pond by water-fowl. 

 In order to obtain the nutritious seeds these birds break open the fruits of Water- 

 lilies with their bills, and in so doing are almost sure to leave some of the seeds, 

 which are imbedded in a slimy mass, sticking to the feathers surrounding their 

 bills. If they are suddenly disturbed at their meal they have not time to clean 

 their bills before fljnng away, and so they carry the seeds with them, and do not 

 rub them off tiU they reach another pond. 



The fruits and seeds of several plants attach themselves to any animals that 

 happen to brush against them by means of special glandular hairs or stalked glands. 

 These latter consist of round cells or groups of cells which are borne on stalk-like 

 structures springing from the epidermis, and which produce on their surfaces viscid, 

 slimy, and resinous substances (see figs. 476 ^ and 476 *). The most diverse parts 

 may be clothed with stalked glands. In Boerhavia, Adenocarpus, and Pisonia (see 

 fig. 476 *), it is the pericarp; in Salvia glutinosa (fig. 476 ^), and the various species of 

 the genus Plumbago, such as Plumbago Gapensis (fig. 476^), it is the calyx; and in 

 Linncea horealis (figs. 476** and 476^) it is a pair of bracts closely adherent to the 

 fruit that is beset with stalked glands. In all these plants an absciss-layer is 

 formed in the tissue of the fruit-stalk, and as soon as adhesion takes place the fruit 

 is severed from the plant at the region of this separating or absciss-layer. Many 

 plants— as, for example, the annual Cerastium glutinosum — have glandular hairs 

 all over them, and when the seeds are ripe and the plants partially withered and 

 only loosely rooted in the ground, a touch is sufiicient to cause leaves, stems, and 

 fi-uits to stick to the hair or feathers of any animal that may happen to pass. 

 We may add that, in the case of every plant above refeiTcd to for illustration, the 



