y-i FUNGI. 



dissolution of a cross-wall (generally of a mucilaginous nature). 

 The individual links of conidia-chains are detached from one 

 another in the same way, or often by means of small, intercalary 

 cells, which are formed at the base of the individual links, and 

 becoming slimy, dissolve upon the maturity of the spores. 

 Special contrivances for ejecting the spores and conidia may often 

 be found. In Peronospora the cylindrical fruit-hyphaa in the dry 

 condition become strap-shaped and also twisted. These are very 

 hygroscopic, and the changes of form take place so suddenly, that 

 the spores are violently detached and shot away. In Empusa a 

 peculiar squirting mechanism may be found (Fig. 85). Each club- 

 shaped hypha which projects from the body of the fly, bears a 

 conidium at its apex ; a vacuole, which grows gradually larger, 

 is formed in the slimy contents of the hypha, and the pressure 

 thereby eventually becomes so great that the hypha bursts at its 

 apex, and the conidiam is shot into the air. By a similar mechan- 

 ism, the spores of many of the Agaricaceae are cast away from 

 the parent-plants. In the case of Pilobnlus (Fig. 84) the entire 

 sporangium is thrown for some distance into the air by a similar 

 contrivance, the basal region of the sporangium having, by the 

 absorption of water, been transformed into a slimy layer which 

 is readily detached. Sphcerobolus, a Gasteromycete, has a small, 

 spherical fruit-body (basidiocarp), the covering of which, when 

 ripe, suddenly bursts, and the basidiospores contained in it are 

 forcibly ejected. 



The spores ichich are enclosed in asci are, in some instances, set 

 free from the mother-cell (ascus) prior to their complete develop- 

 ment (Elaphomycet, Enrotiuni). In the case of the majority of the 

 Pyrenomycetes and Truffles, the asci swell by the absorption of 

 water into a slimy mass, which gradually disappears, so that the 

 spores lie free in the fruit-body ; they either remain there till the 

 fruit- body decays, as in those which have no aperture (Perisporiaceae, 

 Tuberaceae), or the slimy mass, by its growth, is forced out through 

 the aperture of the sporocarp, taking the spores with it (Nectria). 

 The ejection of the spores by mechanical means takes place in a 

 number of Ascomycetes, and should many spores be simultane- 

 ously ejected, a dust-cloud may be seen with the naked eye to 

 arise in the air from the fruit-body. This is the case in the larger 

 species of Pe:iza, Helvella, Rhytisma, when suddenly exposed to a 

 damp current of air. A distinction is drawn between a simultaneous 

 ejection of all the spores contained in the ascus, and an ejection at 



