44 A MANUAL OF THE ASPERGILLI 



A comparatively thin spore suspension is spread on an agar surface, and 

 single well-separated spores are located with the microscope. A small 

 cutting device, mounted on a holder screwed into the nose-piece of the same 

 microscope, is lowered into the agar and a small block bearing the selected 

 spore is removed. This is subsequently transferred to a suitable culture 

 surface where the colony develops. 



At the Northern Regional Research Laboratory we have employed a 

 somewhat different and simpler method. A thin spore suspension is spread 

 evenly over the surface of a firm agar gel that has been specially filtered to 

 remove all particulate matter. This is incubated overnight and the spores 

 allowed to germinate. On the following day, well-separated sporelings are 



Fig. 11. Single spore isolation. A, A single, well-isolated, germinated conidium 

 of Aspergillus niger. B, The same removed on a small agar block and transplanted 

 to a fresh agar plate as described in the text, p. 44, X 300. 



located with the aid of a microscope and their positions marked on the 

 under-surface of the culture dish. These are then checked with a 8 mm. 

 objective and 10 X or 15 X oculars to insure that there are no other un- 

 germinated spores in the same area. Using a wide-field binocular of the 

 Greenough type and very small micro-scalpels fashioned out of platinum- 

 iridium wire (B and S gauge 22 or 24), small agar blocks on which the spores 

 spores rest are transplanted to fresh agar plates. Each of these agar blocks 

 is then examined again with the 8 mm. objective to insure that the selected 

 spore has been transplanted. An experienced worker can isolate from 25 

 to 30 spores within a period of an hour. Photographs showing essential 

 steps in this technique are presented in figure 1 1 . 



