LITTLE-KNOWN PLANTS 165 



Mushrooms are an important crop raised by mar- 

 ket gardeners. Since these plants grow in the dark, 

 they are often raised in caves and cellars and under 

 benches in greenhouses. These plants, having no 

 green parts, must have ready-made food ; and so the 

 soil for mushrooms must contain a large amount of 

 organic matter. While mushrooms are reproduced 

 from spores, yet the usual method of propagation is to 

 take small masses of the compost in which are the under- 

 ground parts of the mushroom and plant these in the 

 new mushroom beds. Each little cube of dried com- 

 post containing the white threads is called mushroom 

 spawn. 



Hops. In parts of the United States, hops are an 

 important crop. Hop plants are vines that are grown 

 on poles. The hops are picked and pressed into bales 

 for market. These pods, called hops, are used in 

 brewing to flavor beer. 



QUESTIONS 



1. What plants yield spices ? 



2. What is rubber ? How is it obtained ? 



3. What plants are valuable because 01 their medicinal 

 properties ? 



4. What plants yield tannin ? What use is made of this 

 product ? 



5. What plants are grown for the flavoring extracts that are 

 made from them ? 



6. How are mushrooms raised ? 



7. What use is made of hops ? 



