1918-19.] BOTANICAL SOCIETY OF EDINBURGH 335 



The Preservation of Artificial Cultures of Moulds, 

 By Harry F. Ta(jg, F.L.S. 



(Read 10th A])ril 1919.) 



A culture of a mould on nutrient gelatine or agar-agar 

 may be killed with formaline vapour, and if it then be 

 sealed up in the Petri dish in which it grew it will keep 

 indefinitely, provided sufficient formaline vapour is present 

 to prevent chance infection from the outside during the 

 sealing process. The method ceases to be satisfactory when 

 the mould is one that causes liquefaction of the medium on 

 which it grows, because when this is the case the Petri 

 dish cannot be tilted from the horizontal position. With 

 cultures that are to be exhibited in a museum it is a dis- 

 tinct gain to be able to display thein tilted at any desired 

 angle, and with class specimens also it is an advantage to 

 be able to handle them freely. 



In the case of species that do not liquefy the medium, the 

 latter may be cut out of the dish with the culture attached 

 and dried down on a square of glass or stiff card. Cultures 

 thus dried make useful reference specimens. The method 

 has been advocated as a simple way of preparing herbarium 

 specimens of artificial cultures grown on agar-agar.^ It 

 has the disadvantage where museum specimens are con- 

 cerned and appearance is of importance that the surfaces 

 of cultures tend to crack into discontiguous areas as the 

 jelly matrix shrinks. 



In the preparations now exhibited the difficulties associ- 

 ated with liquefaction of the medium and the areolation 

 resulting from the contraction of the medium in the case 

 of cultures that are dried, are alike avoided by the removal 

 of the medium altogether. This has been done by floating 

 the cultures on the surface of a dish of water warmed up 

 sufficiently to cause the medium to melt. This method has 

 given excellent results with cultures grown on gelatine, but 

 is not so well suited to the preservation of agar cultures 

 because of the slow solubility of the latter medium. In 

 carrying out the method the procedure is as follows : — 



1 Hedgcock and Spaulding, Journal of Mycology, xii (1906), p. 147. 



