826 THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



conidia, they stick to it so firmly that it cannot succeed in getting rid of them or 

 freeing itself in spite of all its attempts. Eacli adhering conidium then again sends 

 a tube into the body-cavity of the fly, and the development is repeated in the way 

 just described. The same thing happens in Entomophthora radicans, which lives on 

 the caterpillar of the Common White butterfly (Pieris Brassicce). It is represented 

 in figs. 383 ^' ^' ^' *■ ^, p. 672). Tufts of delicate thread-like hyphas come out of tho body 

 of the caterpillar for the purpose of forming conidia (fig. 383'). These gradually 

 form a thick web round the dying caterpillar, and at a cursory glance one might 

 think it had woven its covering and changed into a chrysalis (fig. 383 ^). The tubes, 

 looking like fine threads, unlike those of Empusa, are here much-branched, and 

 actual tufts of hyphse arise from whose ultimate somewhat swollen ends the long, 

 sticky conidia are abstricted and scattered (figs. 383 * and 383 ^.). 



The scattering of the spores from the asci of Ascomycetes takes place in a 

 characteristic manner. They are developed in groups of 2, 4, 8, 16, or 32 in the 

 tubular asci, and numerous thread-like hyphal ends, the so-called paraphyses, occur 

 between the asci (see fig. 456 ^). In addition to the spores the asci contain proto- 

 plasm and cell-sap, and are considerably distended by the large amount of the 

 latter. As the dilatation increases the asci burst, and their cell- wall, which is at a 

 high tension, exercises a powerful pressure on the cell-contents, which are extruded 

 with great force. The place where the rupture of the wall of the ascus occurs is 

 determined beforehand, so that the extrusion of the cell-contents and spores always 

 takes place in the same way. In many species the top part of the ascus-wall is 

 raised like a lid, in others a transverse splitting occurs, and in others again the 

 spores are ejected through a small circular hole. A slight shake or a dry breeze is 

 quite enough to cause the ejection, and in Spatularia flavida, for example (figured 

 on p. 791), or in Peziza aurantia (see fig. 456'), it is easy to observe how small 

 clouds of extruded spores rise from the surface of the fructification as soon as these 

 Fungi are brought from a damp place into a dry atmosphere, or when a dry wind 

 blows over them. In some species of Ascobolus, minute black or waxen yellow 

 Fungi living on the excrement of animals, the spores are not only ejected, but the 

 turgidity of the tissue surrounding the tubes is so great that the whole tubular 

 layer is extruded with the spores. 



Some Gasteromycetes have special contrivances for scattering the spores. In 

 species of the genus Oeaster (see figs. 391 * and 391 ®, p. 690) the threads of the capil- 

 litium and the spores imbedded between them develop within a tough, leathery, 

 bladder-like envelope which separates into two layers when the spores are ripe. 

 The inner layer has the form of a bladder, and opens only at a spot at the apex. 

 The outer layer, on the other hand, splits into 4-12 radiating lobes. The position of 

 the lobes alters remarkably according to the hygroscopic condition of the atmo- 

 sphere. In damp weather they fold together over the vesicle, but in dry weather, 

 especially in sunshine and when a dry wind is blowing, they bend back so forcibly 

 that some of the spores are shaken from the mouth of the vesicle. Travellers in 

 Central America tell us of the gigantic PufF-balls which literally explode on being 



