38 HOLTERMANN : FUNOUS CULTURES 
Modern mycology operates in Europe principally with 
very fluid nutrient solutions. As is mentioned on page 2 of 
the introduction to my ‘‘ Mycologische Untersuchungen,” 
such were but little used in my work. For as the cultures 
even in moist chambers are easily exposed to evaporation, 
the nutritive solution must be supplied in a form in which 
its concentration and composition may remain unaltered. I 
employed an addition of various Tremella or Auricula decoc- 
tions with good results. The mass appeared almost as clear 
as water, and possessed more or less viscosity according to the 
concentration, but, finally, I was successful in the hottest 
season atBuitenzorg with a little gelatine. The nutritive sub- 
stratum is not rendered solid by the addition of the gelatine 
as in our climate, but in the warm tropical regions remains 
always more or less viscous. To prepare a firm substratum 
it is necessary to add a mixture of agar-agar with gelatine. 
Obviously, in employing viscous fluids, the jet of the flask (c) 
must be correspondingly enlarged, or better, the flask may be 
slightly warmed till the solution has the necessary fluidity. 
The influence of daylight on the cultures, especially in the 
tropics, is very injurious, and they must therefore be kept 
in semi-darkness. The injurious effect is to be chiefly at- 
tributed to the fact that the solution loses water in light, 
thus producing an unsuitable degree of concentration. It is 
the more necessary to protect the cultures from evaporation, 
as a subsequent addition of solution is disadvantageous, the 
currents thus induced often affecting the culture. To ob- 
tain absolutely pure cultures is an operation attended by 
great difficulties, and in the tropics particularly, if errors are 
to be avoided, it is necessary to work with extreme care and 
cleanliness. A culture should contain only one species. A 
strange germ is capable within a short time of altering and 
destroying this. Certain fungi, e.g.^ some'Dacryomycetes, 
showed themselves, however, capable of overcoming all intru- 
ders, even Pénicillium, which as a rule destroys everything. 
Botanical Institute of the Royal University, 
Berlin, Autumn, 1901. 
