no RESEARCHES ON FUNGI 



There is perhaps no very obvious answer to this question. The 

 large number of cystidia and the way in which they cross the inter- 

 lamellar spaces of as yet unexpanded fruit-bodies suggest that they 

 serve as organs for maintaining the existence of the interlamellar 

 spaces and thus for preventmg the opposing surfaces of adjacent 

 gills from rubbing on one another during the development of the 

 first spores. If this function is the true one, then we have a 

 physiological similarity with what obtains in Coprinus atramentarius 

 and certain other Coprini.^ The cystidia in the young unexpanded 

 fruit-body often completel}^ cross the interlamellar spaces, but the 

 hooks do not become entangled in the hymenium of the opposing 

 gill (cf. Fig. 49, D, p. 106). The hooks on a cystidium are always 

 produced apically and are turned outwards : thus they increase the 

 surface of the end of the shaft. Possibly, therefore, the shaft is 

 thereby better fitted to push against the opposing gill and thus to 

 maintain the existence of the interlamellar space. There seems to 

 be no evidence that the sharp hooks are used to penetrate anything. 

 Another fact which supports the idea that the cystidia are inter- 

 lamellar space-makers is that the wall of that part of each cystidium 

 which projects across an interlamellar space is much thickened and 

 thereby greatly strengthened mechanically {cf. Fig. 51, p. 108). 



Stahl found that the acicular raphides which occur in bundles 

 in the leaves of many Monocotyledons, e.g. Arum maculatum., render 

 the leaves inedible to slugs, owing to the fact that they irritate the 

 mucous membrane of the mouth in a mechanical manner.^ It 

 struck me that possibly the hooked cystidia might have a similar 

 protective function. I therefore collected slugs of three species 

 from the garden and, after starving them for a few hours, offered 

 them pieces of the pileus of Pluteus cervinus to eat. One of the slugs 

 {Limax maximus ?) ate freely of the gills, and must have devoured 

 thousands of cj^stidia. Dr. W. T. Elliott found that, under 

 laboratory conditions, the fruit-bodies of Pluteus cervinus are readily 

 eaten by Limax maximus and L. cinereo-niger, and slightly eaten 

 by Arion ater.^ The hooked cystidia do not therefore appear to be 



^ Vide infra. 



^ E. Stahl, Pflanzen und Schnecken, Jena, 1888, p. 85. 



^ W. T. Elliott, in litt. 



