FUNGUS GNATS 19 



structures with narrow necks each provided with a tiny operculum. 

 He states that the opercula drop off when the cystidia are mature, 

 and thus permit the cell-contents to escape. According to both 

 Smith and Massee, the cystidia in many cases drop out of the 

 hymenium after they have discharged their contents. A detailed 

 confirmation or refutation of these various statements seems to 

 me to be desirable. 



In a recent paper Massee l has described two forms of cystidia 

 as occurring on the surface of the gills in the genus Inocybe — the 

 ventricose and the fusoid. He states that the tip of each cystidium 

 becomes crowned with mucilage, which escapes from the interior 

 after the deliquescence of the thin portion of the wall at its apex. 



From the morphological point of view, we may follow de Bary 

 in placing cystidia in the category of hair formations. Since the 

 hymenial hairs are of several distinct types, it seems fairly certain 

 from analogy with the Phanerogams that they have different 

 functions varying with their structure. In some species they 

 may be only functional during the early development of the gills, 

 whilst in others they may be of importance afterwards. 



From the point of view of spore-emission, cystidia have a limit 

 set to the distance they may project beyond the basidia. Where 

 a hymenial surface is in a vertical plane, they only project so 

 far that they do not interfere with the falling spores. These are 

 shot out horizontally from the basidia to a distance of about 

 01 mm. They then make a sharp turn and fall down vertically 

 (cf. Fig. 64, p. 185, and Plate I., Fig. 4). Since the cystidia do 

 not project so far horizontally as the spores can be shot outwards, 

 they do not restrict the freedom of the latter whilst escaping from 

 the fruit- body. 



Fungus Gnats, Springtails, and Mites. — Possibly in some 

 instances cystidia may have become evolved in relationship with 

 insects or other small animals. Over one hundred and fifty 

 species of Mycetophilida) or "Fungus Gnats" have been described, 2 

 and most of them appear to live on fungi only. 3 The whole group 



1 G. Massee, ' ; A Monograph of the Genus lnocyhe, ' Ann. of Bot , vol. xviii., 

 1904, p. 462. 



2 Fred. V. Theobald, An Account of British Flics (Dipter.i), vol. i., 1892, p. 93. 



3 Ibid., p. 96. 



