12 



RESEARCHES ON FUNGI 



when isolated from 



Fig. 5. — Lepiota cepae- 

 stipcs. A vertical 

 section through three 

 gills of an expanded 

 pileus (cj. Fig. 2, 

 right), during tlie dis- 

 charge of the spores. 

 The gills are wedge- 

 shaped and look ver- 

 tically downwards. 

 There are marginal 

 hairs (cystidia) at the 

 free margins of the 

 gills. The trajec- 

 tories of a number of 

 spores which have 

 been shot from the 

 hymenium are indi- 

 cated by the arrows. 

 The peculiar struc- 

 ture of the trama and 

 the loose texture of 

 the pileus-flesh are 

 indicated. Magnific- 

 ation, 20. 



the trama, curl up in the manner shown at D. 

 Some of the strips so curled up resemble 

 watch springs. The hymenium, when given 

 the opportunity, expands more than the 

 underlying subhymenium. When forming 

 part of a normal gill, therefore, it must be 

 in a state of compression. Where a transverse 

 section does not extend to the gill-edge, as 

 at A, or is taken out of a gill, as at C, the 

 opposing outer strips (made of hymenium and 

 subhymenium), where not attached to tramal 

 cells, curl over toward each other and become 

 crossed. It is evident that the two opposite 

 outer sheets of each gill tend to become 

 convex toward the inter-lamellar spaces which 

 they face. In an intact fruit-body, however, 

 they are prevented from attaining this con- 

 vexity because : (1) at their bases, along the 

 line of the free gill-margin, they are joined 

 to each other in pairs, (2) they are held in 

 check in their middle parts by the transverse 

 tramal cells, and (3) at their tops, where they 

 adjoin the pileus-flesh, they are continuous 

 with similar sheets on adjacent gills. The 

 sheet of cells, which makes up the hymenium 

 and subhymenium on the under side of the 

 whole pileus, is corrugated symmetrically 

 about the pileus-centre. The stresses and 

 strains in the sheet during the expansion of 

 the pileus are such as tend to flatten out the 

 corrugations and, doubtless, to some extent 

 at least, they assist in the expansion of the 

 pileus and the separation of the gills from one 

 another. The tendency which the sheets 

 have to create interlamellar spaces may be 

 gathered from the loop which has been 

 formed between the two gills shown in 



