OABPOPIiTTA. 191 



(e) Make thin vertical sections through one of the fruiting disks, 

 mount as above, and study spore-sacs, spores, and paraphyses. 



(/) Collect some of the small, flat, many-Iobed lichens which grow 

 on the bark of apple-, maple-, and oak-trees, and having small black- 

 ish fruit-disks. Make careful sections of the plant-body through the 

 fruit-disks, and study the whole structure, spores, spore-sacs, para- 

 physes, filaments, and gonidia. (Compare with Fig. 110.) Here also 

 the gonidia closely resemble Green Slime. 



( g) Collect fresh specimens of Plum Pockets, and preserve them in 

 alcohol. Study the fungus by making very thin sections at right 

 angles to the surface. Each spore-sac will be found to contain 

 several rounded spares. 



(h) Fill a strong bottle half full of active yeast, cork tightly, and 

 keep for an hour or two in a warm room. Draw the cork and notice 

 the violent escape of gas (carbon dioxide). 



(i) Place a small drop of the yeast upon a glass slide, add a little 

 water, cover with a cover-glass, tapping it down gently. After a 

 little examination under a high power of the microscope add iodine, 

 which will stain the starch-grains blue or purple, and the yeast- 

 plants yellowish. Many of the latter will be found in process of 

 budding, as in a andS, Fig. 113. 



(j ) Spread a half-teaspoonful of yeast on a fresh-cut slice of potato 

 or carrot ; cover with a tumbler or bell-jar to keep it moist ; after a 

 few days (four to eight) examine for cells which are producing spores, 

 as in c and d. Fig. 112. 



Systematic Literature. — Saccardo, Sylloge Fungorum, 8 : 3-859, 

 916-933. Tuckerman, Synopsis of the North American Lichens, 

 1. 3. 



352. The Rusts (Order 16. Ukedine^) are minute, 

 parasitic, degraded sac-fungi which grow in the tissues of 

 higher plants. Their life-history is only imperfectly known, 

 nothing as yet being known as to their sexual organs, if 

 indeed they have any. 



353. The common Wheat-rust (Puccinia graminis) may 

 be taken as an illustration of the order. It is common 

 wherever wheat is grown, and often greatly injures and 

 sometimes entirely destroys the crop. Its round of life 

 shows four well-marked stages, as follows: (I) In the spring 

 clusters of minute yellowish cups break through the tissues 



