PLANT GROUPS 259 



theria, tuberculosis, and pneumonia, are caused by the at- 

 tacks of certain minute Fungi trying to obtain their food 

 from our bodies. In doing this, they either destroy some of 

 our body or give off substances that poison us. Some of 

 these Fungi do not attack living bodies, but use for food 

 dead bodies or material that has been made by living 

 bodies. For example, you may have seen bread that has 

 become "mouldy." This means that one of these Fungi 

 has attacked the bread to get its starch (see Fig. 46). You 

 know about yeast. It is one of these Fungi that attacks 

 sugar, and in so doing gives off a gas that puffs up bread- 

 dough and makes it " light." 



You will see that the Algae are very interesting, because 

 they are our first independent plants, independent because 

 they are green and can make their own food. The Fungi, 

 however, are more important to us because they so often 

 produce diseases from which we suffer, and also diseases 

 that injure our valuable animals and plants. 



2. The First Land-Plants. The second story of our 

 plant apartment-house is occupied by the first land-plants. 

 The Algae live in water or in very moist places. They 

 could not take possession of the land. But from the Algae 

 the first land-plants came. You have seen mosses, which are 

 the most common members of this group. They are found 

 very abundantly in shady and moist places, and some of them 

 are able to live in very exposed places, as on bare rocks. 



The plants that first learned to live on land, however, 

 were not mosses, but the relatives of mosses known as liver- 

 worts (see Fig. 91). You will find them in moist and 

 shady places, sometimes clinging to rocks or tree-trunks, 

 but sometimes growing flat on the ground. 



