1 64 MUCOR 



then stirred round in the drop of Pasteur's solution, so as to 

 sow it with spores. By this method the drop of nutrient 

 fluid is prevented from evaporating, and the changes under- 

 gone by the spores can be watched by examination from time 

 to time under a high power. 



The first thing that happens to a spore under these con- 

 ditions is that it increases in size by imbibition of fluid, and 

 instead of appearing bright and clear becomes granular and 

 develops one or more vacuoles. Its resemblance to a 

 yeast-cell is now more striking than ever. Next the spore 

 becomes bulged out in one or more places (c 1 , Fig. 36), looking 

 not unlike a budding Saccharomyces. The buds, however, 

 instead of becoming detached increase in length until they 

 become filaments of a diameter slightly less than that of the 

 spore and somewhat bluntly pointed at the end (c 2 ). These 

 filaments continue to grow, giving off as they do so side 

 branches (c 3 ) which interlace with similar threads from 

 adjacent spores (H). The filaments are obviously hyphse, 

 and the interlacement is a mycelium. 



Thus the statement made in a previous paragraph (p. 161), 

 that Mucor was comparable to a yeast -cell pulled out into a 

 filament, is seen to be fully justified by the facts of develop- 

 ment, which show that the branched hyphse constituting the 

 Mucor-plant are formed by the growth of spores each strictly 

 comparable to a single Saccharomyces. 



It will be noticed that the growth of the mycelium is cen- 

 trifugal : each spore or group of spores serves as a centre 

 from which hyph?e radiate in all directions (H), continuing 

 to grow in a radial direction until, in place of one or more 

 spores quite invisible to the naked eye, we have a white 

 patch more or less circular in outline, and having the spores 

 from which the growth proceeded in its centre. Owing to 

 the centrifugal mode of growth the mycelium is always 



