276 THE AMERICAN MONTHLY [Aug. 



ing Pasteur's fluid in which theconidia of Penicillium have 

 been sown at dift'ereiit times. Compare them with a ves- 

 sel in which conidia have been sown merely in water. 

 Note the white spots, colonies, which appear on the sur- 

 face of Pasteur's fluid, their daily increase in diameter, 

 the appearance of a greenish spot in the centre of each 

 and its increase in size ; the fusion of the colonies as 

 they reach eacli other to form a mat, mycelium, gradually 

 growing denser and completely covering the culture fluid; 

 the formation on older mycelia of a greenish dust, coni- 

 dia, which can easily be blown into air. Note that the 

 color is a bluish green, not identical with the color of 

 chlorophyll. 



Mount a very small colony, or a piece cut out of a lar- 

 ger one and examine first uncovered, I. p., you can recog- 

 nize the fine branching fibers, hyphae, of which it is com- 

 posed; some of these stand upright and carry a broom- 

 shaped portion bearing the greenish powdery conidia. 

 With needles tease the fibres apart, replace the water 

 with 50 per cent alcohol, cover and examine, h. p., search 

 for single fibres and study them. Make an iodine stained 

 mount, and study that in connection, using it for compari- 

 son with the other. Determine first the shapes and posi- 

 tions of the cells. Do you find cross walls? Do the cells 

 branch? At what part of the cell does the branch arise ? 

 Is the cell filled with protoplasm, or are there vacuoles ? 

 Do you find fat droplets? Can you find any nucleus ? 

 Is there any indication of the presence of chlorophyll ? 

 Is there any indication of a cell-ioall? Study the termin- 

 ation of hyphae and compare them with the older por- 

 tions of the same ? What similarities and diff'erences can 

 you find ? 



Find the broom-shaped growth at the tips of some of 

 the hyphae, it is the part devoted to the production of 

 conidia. Locate the string of conidia. How many are 

 there in a row ? Are all of the same size ? Do the rows 



