22 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



have .shown these to be much more important in flowering plants 

 than was formerly supposed. The introduction of these characters 

 is thus in full conformity with the best systematic practices of 

 to-day, where the life history of the species is investigated as fully as 

 possible. 



CULTURE MEDIA. 



In developing the descriptions presented the following media have 

 been used: 



1. Potato agar. This was made as described in another paper 25 

 (p. 7). Essentially this is simply a potato infusion to which agar- 

 agar is added in any proportion desired. Since this medium is free 

 from sugar and very dilute in nutrient value, sugar may be added to 

 cultivate certain species. 



2. Bean agar. The directions for making bean decoction were 

 obtained from Maze at the Pasteur Institute in Paris. Common 

 white beans are heated in five volumes of water. Boiling is stopped 

 just before the swelling of the cotyledons would rupture the seed 

 coats. This gives a clear, slightly yellowish liquid which filters 

 readily yet contains sufficient nutrients to grow many species nor- 

 mally. Agar may be added as desired. Since this decoction is 

 poor in available carbon, the addition of sugar is often desirable for 

 many species. 



3. Peptone-milk sugar-gelatin, as described by Conn. 4 This stand- 

 ard bacteriological formula, with and without litmus, w r as used in 

 developing the original draft of these descriptions. 



4. Fifteen per cent gelatin in distilled water. As a stock medium, 

 this w T as used without neutralization. Comparative cultures neu- 

 tralized with NaOH seemed less adapted for most species than un- 

 changed gelatin. With few exceptions the common species of 

 Penicillium grow readily in plain gelatin and give the same reaction 

 as in Conn's more complex formula. 



5. Synthetic media. A. W. Dox, chemist to this investigation, 

 has modified Czapek's formula for a synthetic medium, intended to 

 present in a nearly neutral solution unaffected by sterilization the 

 elements necessary for fungous growth. In stock form neither nitro- 

 gen nor carbon is presented in this fluid. It has consequently been 

 found an excellent means of testing the availability of these elements 

 in various forms. For convenience this will be referred to as Dox's 

 solution, the formula of which is — 



Distilled water centimeters. . 3, 000. 



Magnesium sulphate grams. . 1. 5 



Dipotassium phosphate (K 2 HP0 4 ) do 3.0 



Potassium chlorid do 1.5 



Ferrous sulphate do .03 



