34 OUTLINES OF PLANT LIFE. 



EXERCISE VIII. 



Black mold (Rhizopus nigricans). — Before any white or black dots ap- 

 pear on the mold examine the vegetative hypha. (^ 41.) These are of 

 two kinds, (a) those running over the surface of the bread ; [b) those 

 penetrating it. 



1. Examine a. Lift up a few threads with a needle and mount them 

 in water. Study with a lens. Are they white or colorless? Why 

 then is the body composed of them (the mycelium, ^ 4.3) white ? 



2. Examine b. With needles tease out hyphse from a bit of bread in 

 water ; free them as far as possible from the dfebris and mount. Com- 

 pare with a. 



After mold has begun to show black dots [spore cases, \ 271) examine 



3. Determine how the branches are placed which bear the spore cases. 

 (Fig- 30-) 



4. Compare the white (young) and black (mature) spore cases. Can 

 you find the very smallest ones ? 



5. Snip off a few ripe spore cases with scissors, handling them cau- 

 tiously to avoid breaking or tangling them ; mount in alcohol * and ex- 

 amine. Crush (if not already broken) and observe numerous dust-like 

 particles, the spores, which escape. (Fig- 146.) 



44. Parasites. — Especially is this true of those fungi 

 which grow in the interior of living organisms. The higher 

 plants are liable to be fastened upon by parasitic fungi, and 

 compelled to act as hosts to their unbidden and unwelcome 

 guests. Such a host plant may be entered when a mere 

 seedling, in which case the fungus grows with its growth, or it 

 may not be attacked until older or even mature. The host 

 may be permeated in all its parts by the fungus filaments ; or 

 certain members only, such as the leaves, flower parts or 

 twigs, may be affected. The effect of the fungus upon the 

 host is often scarcely visible to the unaided eye ; sometimes 

 a local disturbance is manifested by swelling, unnatural color 

 or growth ; sometimes the affected members become distorted 



* Because water will not wet them. Replace alcohol as it evaporates ; 

 it does so rapidly. 



