Fungi 409 



the hyphae and rhizoids. The rhizoids secrete enzymes in the 

 bread, which change the starch, fat, and protein into various 

 soluble substances that diffuse into the fungus hyphae and pass to 

 all parts of the mycelium. Try an experiment with a small 

 piece of moist bread in a covered tumbler and see how long it 

 takes for the bread to be consumed. These molds are for the 

 most part saprophytes. 



There are molds, however, that are both parasites and sapro- 

 phytes. Perhaps you have seen goldfish growing in an aquarium, 

 that were given to turning sidewise somersaults in the water and 

 rubbing their sides on the gravel in the bottom of the jar. You 

 may also have noticed cobwebby filaments attached to their 

 scales; perhaps there were enough of them to make the sides 

 appear white. This growth is one of the water molds (Sapro- 

 legnia) common in ponds and streams and often a cause of great 

 losses at fish hatcheries. There are other related molds that 

 attack flies and other insects and cause their death. 



THE SAC FUNGI OR ASCOMYCETES 



The sac fungi differ from the tube fungi in being composed of 

 hyphae made up of short cells. They exhibit a great variety of 

 forms, from those like the green molds to fleshy forms like the 

 morels. This is the largest division of the fungi and includes more 

 than 30,000 species. 



The outstanding feature of the sac fungi is the method of pro- 

 ducing spores inside sac-like sporangia called asci (singular, a^cz^^), 

 which are the terminal cells of upright hyphae. Usually the sacs 

 are grouped in clusters ; sometimes they stand upright side by 

 side and form a layer over a part of the plant body. Many 

 species also produce spores that are pinched off at the ends of 

 short hyphae. These spores are called conidia, and are impor- 

 tant in spreading the fungus during the growing season. They 

 may be produced in such abundance that an infected leaf has 

 the appearance of being covered with white powder. 



