168 DR. ETHEL M. DOIDGE 



some ferns, for instance, which are very tliin and brittle 

 when dry, it is advisable to work with the fresh material. 



The method is as follows: — Select a leaf on which the 

 hand lens has revealed the presence of reproductive 

 bodies, with the glass rod put a drop of collodion over 

 the fungus and alloAV it to dry. A little experience will 

 soon show how much collodion to apply, so that a suffi- 

 ciently tough film is formed without its being too thick 

 and opaque. TN'lien the collodion is dry, slip a dissecting 

 knife under the him and raise it carefully — you will 

 notice that the fungus adheres to the collodion — and place 

 it on a glass slide. Dissolve a part of the collodion with 

 the mixture of alcohol and ether, which will also cause 

 the film to adhere to the slide, and allow to dry again ; 

 then flood the slide with xylol, let it run off, put a small 

 drop of balsam on the preparation with a glass rod, and 

 carefully lo^^'er a cover slip over the preparation. If the 

 balsam becomes at all cloudy the collodion has not been 

 thoroughly dried before applying the xylol, and the cover 

 slip can be removed, the balsam removed w^ith xylol, the 

 xylol with a little absolute alcohol, and the preparation 

 re-dried. If there are air bubbles under the cover-slip, 

 which frequently occurs when the fungous growth is par- 

 ticularly dense, these can be removed by heating the slide 

 gently over a small spirit lamp. 



A successful preparation ilepicts the fungus exactly as 

 it grew on the leaf surface. ^Microscopic preparations 

 must be carefully labelled and given the number of the 

 specimen from which they are taken. 



Tfie Fungi. 



I have men Honed above that the majority of the black, 

 su])erficial leaf fungi belong either to the family Peri- 

 S]KJ)'i((('('ae or to the Microtlnirinccac. In describing ^he 

 cliier clinractf^'istics of these \\\o families it will be neces- 

 sary to iiiti'oduce a few leclmical terms, wliir-h, however, 

 sliould not i)resent any dilticulty Avhen fully explained. 



The hjipliac are the spreading vegetative threads of the 

 fnngiis, wliicli are referred to collectively as the myce- 

 liiiin. 



