246 ESSENTIALS OF BOTANY 



becomes still lighter as the gas expands in the oven. Cakes 

 of compressed yeast are nowadays generally used in bread 

 making. It is important that they should be as fresh as 

 possible, since when they are old they are likely to contain 

 some wild yeasts and many bacteria. These are pretty sure 

 to injure the quality of the bread made from such yeast. 



RHIZOPUS, ONE OF THE ALGAL FUNGI 



317. Occurrence. — The common bread-mold, RMzopus 

 nigricans, is found upon bread or cake left in a warm 

 damp place, or on sweet potatoes, squashes, or bananas. 

 Its spores are likely to be present in the dust of houses, 

 and many lie dormant for months, producing when they 

 alight on favorable food material a luxuriant crop of the 

 downjr coating of white silky threads so familiar to all. 



318. Gross Structure. — Place some bread ^ in a soup plate, wet 

 thoroughly, cover with a bell-glass, and leave for some days in a dark 

 warm place, renewing the water if necessary. When a considerable 

 growth of mold has appeared, examine with the magnifying glass an 

 undisturbed portion as it grows from the surface of the bread. Note : 



(a) The tangled network, or mycelium, visible on the surface of 

 the bread (and really extending a good way down into it). 



(i) The size and appearance of the separate threads, or hyphcc, of 

 which the mycelium is composed. 



(c) The presence of certain erect aerial hyphse bearing minute 

 globular spore-cases at their tips. Describe the color of the youngest 

 spore-cases and that of the largest and oldest ones. 



319. Minute Structure. — Wet a little of the mold with alcohol (to 

 remove the air from it) and then mount in water and examine with 

 m.p. Note : 



(a) The mode of growth of the hyphpe, whether branched or 

 unbranched. 



1 Gluten bread is particularly adapted for this culture. 



