PROBLEM 2. The Kinds of Plains of 



at first looks like an ugly mass is really 

 a very delicate simple plant. In fact, the 

 bread may serve as a garden for several 

 species of beautiful mold plants. The 

 commonest one, known as the bread 

 mold or Rhizopus (ry'zo-pus), consists 

 of a miniature jungle of very fine, glis- 

 tening, white threads. Little black balls 

 appear at the tips of upright threads. 

 These make the mass of white threads 

 look gray and later sooty. 



You can raise a variety of molds by 

 doing Exercise 3. Molds grow on many 

 different foods if enough moisture is 

 provided. There are some mold plants 

 that look like patches of bright blue- 

 green felt; others are salmon pink. The 

 drug penicillin is prepared from some of 

 the blue-green molds. In these the threads 

 are shorter and even more interlaced so 

 that without a powerful lens you cannot 

 see separate threads at all. 



A plant that is both alga and fungus 

 in one. Strictly speaking, this "plant" is 

 two separate plants, one an alga, the 

 other a fungus, but they are so closely 

 combined that they look like one plant. 

 The combination is called a licheii (ly'- 

 ken) . It looks grayish or yellowish green. 

 You may have seen lichens on rocks or 

 trunks of trees. Some, like the "reindeer 

 moss," grow on the ground. 



Lichens are extremely hardy plants; 

 when all else has been killed by the cold 

 they still survive. They are food for 

 grazing animals, such as reindeer, of the 

 arctic zone. Some are eaten by man. 



Fungi that help man bake and brew. 

 The yeast plant is so small and so simple 

 that even under the microscope it does 

 not look like much of anything. It is 

 merely a tiny, colorless, tg^ or rod- 



the Earth 



11 



shaped speck which cannot move. See 

 Figure 362, page 413. It is classified as 

 a plant and is clearly a fungus. 



There is one special kind of yeast that 

 we raise in vast numbers. Millions upon 

 millions of them are pressed into one 

 yeast cake. Yeasts are useful because 

 when they live in sugar solutions they 

 change the sugar into alcohol and a gas 

 called carbon dioxide. This change is 

 called fermejjtation. When we want to 

 bring about fermentation we often put 

 yeast plants with soaked, crushed corn 

 or other grains. When we make wines 

 we add yeast plants to grapes, although 

 until recently we depended on "wild" 

 yeasts to change the sweet fruit juice into 

 alcohol. Wild yeasts and molds, too, float 

 about in the air. You are now ready for 

 Exercises 4 and 5. 



Yeasts, as you may know, are also used 

 in baking. They cause fermentation in 

 the dough but the alcohol evaporates 

 during the baking so you never taste it; 

 the carbon dioxide gas forms bubbles in 

 the solid mass of dough, "raising" it and 

 making it light and porous. 



Bacteria. These very important plants 

 are usually classed as fungi, although 

 some biologists place them in a phyluni 

 by themselves. Most bacteria are so much 

 smaller than yeasts that they are difficult 

 to describe. As a matter of fact, there is 

 probably not much to be seen in them. 

 Most of them cannot move about but 

 some can wriggle when in a liquid and 

 a few can swim by means of long whip- 

 like projections. There are giants and 

 pygmies among bacteria, but even the 

 few giants are so extremely small that 

 they can be seen only with a good micro- 

 scope. It has been calculated that if the 



