35 RESEARCHES ON FUNGI 



away. A drop of water was placed on a glass slide and on this the 

 gill was floated. Another drop of water was then added at the side 

 of the gill, whereupon the preparation was covered with a cover- 

 glass. Under these conditions there was a layer of water between 

 the under side of the gill and the cover-glass. On the upper side 

 of the gill, as soon as the cover-glass had been applied, water began 

 to make its way by capillary attraction over the hymenium, resist- 

 ance to its passage being offered by the sterigmata and spores. 

 When the water passed rapidly over the upper hy menial surface, 

 as sometimes happened, the black spores were nearly all pulled off 

 their sterigmata, whereby the whole preparation was spoiled ; but, 

 with a very gradual passage of the water, the black spores often 

 remained on. Thus, by gradually passing water between the upper 

 hymenial surface and the cover-glass, the former became covered 

 with water without being ruined. The photograph reproduced in 

 Fig. 128 was made from such a water-immersed preparation. 

 In actually taking the photograph, a Leitz microphotographic 

 apparatus was employed. A microscope was fitted with a Leitz 

 ocular, No. 4, and an objective, No. 7 ; and above the tube the 

 camera was placed so that it had a vertical arrangement. The 

 light was given by a Leitz " Lilliput " arc -lamp which was set 

 3 feet from the microscope mirror. The part of the hymenium to 

 be photographed was first focussed in the usual way. The light 

 employed for this purpose came from the arc -lamp ; but, in order 

 to dim its rays, two sheets of glass, one blue and the other yellow, 

 were set in front of it. After the focussing had been accomplished, 

 the camera was swung into position at the top of the tube of the 

 microscope. The piece of hymenium was then focussed on the 

 ground-glass plate at the top of the camera. This plate was then 

 removed and a photographic plate substituted for it. A black sheet 

 of cardboard was next placed vertically against the base of the 

 microscope so as to come between the mirror and the arc-lamp. 

 Then the two sheets of coloured glass, already referred to, were 

 removed from just in front of the arc-lamp. The carbons of the 

 arc were then screwed close together so that the light coming from 

 them was steadied. The cover of the photographic plate was then 

 drawn out. Then, the black sheet of cardboard was lifted away so 



