DISPERSAL BY ANIMALS. 827 



shaken, sending such quantities of reddish spores into the air that it is impossible Uj 

 breathe in their vicinity. In Europe a minute Pufi-ball, Sphoirobolua aUllatus 

 (fig. 456^), grows on decaying stems, leaves, &c. The wall of the fruit divides, 

 as in Geaster, into two distinct layers: one remains closed and a.ssumes the form of 

 a ball, but the outer one when the spores are ripe divides by radiating clefts into 

 several lobes. These bend back rapidly on drying, and as the central portion 

 round which the lobes are placed becomes strongly arched upwards, at the same 

 time the ball containing the spores is shot out with considerable force. 



The dissemination of spores in some of the Ferns is illustrated in figs. 456 •'^' ^ 

 Sporangia are developed on the under surface of the frond, where they are arranged 

 in various ways. Those of the Nephrodium Filix-mas, which is hei-e selected as a 

 type, consist of a stalk and a flattened bi-convex vesicle. Round the latter runs a 

 ring of darker-coloured cells, whose side-walls are much thickened, while their 

 outer walls remain thin and delicate. When the sporangium is ripe its bursting is 

 brought about by the contraction of the cells of the ring. 



With regard to the distribution of ofishoots by animals we may distinguish two 

 classes, those in which the oflfshoots are first conveyed to the animals by special 

 disseminating mechanisms, so that two methods of distribution are combined, and, 

 secondly, those in which animals alone eflfect the transport of the offshoots from 

 one place to another. We have already spoken repeatedly of the former class. Of 

 the latter the distribution of spores by food-seeking animals is the first to be 

 considered. The Pyrenomycetous Fungus known as the Ergot of Rye (Claviceps 

 purpurea) is a well-known instance. The thick web of hyphal threads which 

 invests the ovaries of the Rye is penetrated by labyrinthine passages, whose walls 

 are formed by the ends of hyphal threads arranged in rows and tufts (see fig. 386 -, 

 p. 680). Spherical spores are abjointed from these somewhat club-shaped ends. 

 Simultaneously with this abjunction the outer layer of the cell-wall of both spores 

 and hyphse forms a sugary fluid by the absorption of water and subsequent breaking 

 down. This fills the winding passages, and the innumerable abjointed spores are im- 

 bedded in it. The sweet-tasting fluid gradually collects into drops on the exterior, 

 and even comes into view on the spikes of Rye between the glumes which surround 

 the infected ovaries. This is the "honeydew" by which the presence of the parasitic 

 Claviceps in the interior of the spike is recognized, and which is viewed with some 

 apprehension by the farmer. Insects, especially wasps and flies, eagerly seek out 

 these springs of sweet fluid and suck and lick up the juice, which is crowded witii 

 numberless spores. It is therefore inevitable that small quantities of spores should 

 stick and remain hanging to portions of their bodies, and when they fly to the 

 spikes of other Rye-plants the spores are easily rubbed off", and in a very slu)rt 

 time may again grow up into a mycelium involving the ovaries there. 



A similar phenomenon may be observed in the Phalloidese, belonging to the 

 Gasteromycetes, of which the best known species, the Stink-horn Fungus {Phallm 

 impudicus), may be taken as an example. The cap, borne on a white cylindrical 

 and spongy stalk, is bell-shaped and covered with a greenish-black viscous fluid m 



