ii8 RESEARCHES ON FUNGI 



in pairs. Id Llic courso of two or three hours the gills become 

 perfectly reconstructed, and they are then directed downwards 

 in the normal manner (Fig. 41, E, and Fig. 42). The hymenial 

 layer resumes its activity, and, after three or four hours of access 

 to moisture, the emission of spores is vigorously recommenced. 



The mechanism involved in the closing and opening of a 

 pileus can be partially explained from anatomical considerations. 

 The main mass of each gill plate consists of downwardly running 



Fig. 45. — Schizophyllum commuiu. Above, a transverse section 

 through a half-gill taken in a vertical direction ; below, another 

 transverse section taken in a horizontal direction, h, the hy- 

 menium ; s, the subhymeniuni ; t, the trama ; i, the inner free 

 hairy surface of the half-gill which becomes exposed on desic- 

 cation of the fruit-bodv. Magnilication, 688. 



tramal liyphffi, which have very thick walls and are strongly attached 

 together at intervals. On the other hand, the hymeniuni and 

 subhymenium arc composed of elements with relatively very ihin 

 walls (Figs. 4ri). When a fruit-body dries up, the cell-walls of the 

 hymenial and subhymenial layers contract much more strongly 

 in the vertical direction than those of the tramal layer. This 

 being so, the curling up of each gill plaii:. when water is lost 

 from it, is a mechanical necessity. When a gill reabsorbs moisture, 

 the w'alls of the hymenial and subhymenial layers expand to a 

 greater extent than those of the trama. The tramal hyph.e are 



