THE AMERICAN MONTHLY 



[December, 



phere, which is favorable to the growth 

 of moulds. The blotting-paper pro- 

 motes evaporation wiihin the glass, 

 and thus keeps the atmosphere satur- 

 ated with moisture. 



In a few hours the specimen, if 

 closely examined with a pocket-lens, 

 will be found covered with the threads 

 of mycelium. Scrape the surface with 

 a knife in one spot and put the scrap- 

 ings on a slide, cover it with thin 

 glass, and examine with a I- or i-inch 

 objective. The structure of the my- 

 celium will then be clearly made out. 

 Now let the mould grow until it begins 

 to show itself by its color, which will 

 probably be bluish, as the most ccm- 

 moii ir.r^'d is the blue mould. 



Another way of cultivating a mould 

 for examination is to make a rather 

 strong solution of gelatin in warm 

 water, and spread a thin layer upon a 

 glass slip. The gelatin sets in a clear, 

 transparent film upon which the fun- 

 gus will grow very rapidly in the moist 

 chamber. This method presents the 

 advantage that the growth takes place 

 on a transparent surface, which facil- 

 itates examination under the micro- 

 scope. 



If the mould be examined just be- 

 fore it is seen to change color, using 

 a power of 150 diameters or more, 

 there will be found numerous upright 

 threads standing out from the mass of 

 mycelium. These are fertile threads, 

 and in the common blue mould they 

 will be seen to terminate in distinct 

 heads, which ripen and resolve into 

 innumerable chains of spores, spread- 

 ing outward and bending gracefully 

 downward like the drooping branches 

 of a tree. It is these stems, with their 

 chains of spores, that form the trees 

 of our forest. The spores are the 

 fruit of the mould. Wherever they 

 fall upon a suitable nidus for growth 

 they reproduce the plant. When fully 

 lipe they give the color to the mould. 

 They are so exceedingly minute, how- 

 ever, that they must be examined with 

 a power of 250 diameters. For this 

 purpose some ingenuity must be ex- 

 ercised to get the mould under the 



microscope in good condition for ex- 

 amination. Water dees not readily 

 moisten the li] e spores, and in trying 

 to get a good view cf the stems, \Ailh 

 iheir chains of spores attached, the 

 natural arrangement is suie to be very 

 much bioken up. Peihaps the best 

 way to proceed is to carefully detach 

 a minute portion of the mould with 

 forceps, and lay it gently en a slide. 

 Then moisten it with a few drops of 

 alcohol and water and apply the co\er- 

 glass. Patience and perseverance will 

 doubtless be rewaided by yielding a 

 fine view of the fructification. 



The fungus we have thus briefly 

 described is the blue mould known rs 

 PcniciUiiim, of which numerous species 

 have been described. They are all 

 characterized bv the chains of spores 

 above mentioned, growing from the 

 head of the upright filaments. Bear 

 in mind that the filaments bearing 

 the fruit are distinguished as fertile 

 filaments, and the barren ones form 

 the mycelium. 



Another very common kind of 

 mould is known as Aliicor. In this the 

 fertile stems branch, and terminate in 

 rounded heads within which the spores 

 are enclosed. In FcmciUium the spores 

 are naked, in J///r^r they are protected 

 by a membrane. There is strong 

 presumptive evidence that Alucor and 

 Pen'uilliiim aie different conditions 

 in the growth of the same fungus, 

 but this conclusion is still open to 

 doubt. Conclusive evidence is very 

 difficult to adduce. If a filament of 

 mycelium could be followed in its 

 course until it is found giving rise to 

 both methods of fructification, the 

 conclusion would be undeniable. At 

 present we have only the evidence of 

 close association to support it. If, 

 after the Penicillium has ripened in 

 the moist chamber, the plant be kept 

 under cultivation for a time, it is very 

 likely that Mucor\\\\\ appear, growing 

 up from the same nidus. 



The spores of PcnicilUmn may be 

 sown in a fermentable liquid and they 

 w'll grow precisely like the yeast- 

 plant. It is, therefore, supposed that 



