362 THE NON-VASCULAR PLANTS 



are already familiar with them. The first three groups 

 may be called the non-seed plants. One of our main ob- 

 jects in studying the non-seed plants is to see how, from 

 plants like them, the seed plants have been evolved. In 

 doing this, we shall also gain an acquaintance with these in- 

 teresting groups for their own sake. 



Thallophytes 



These plants fall into two great groups, the alga and 

 the fungi. Algae contain chlorophyll ; fungi do not. 

 Mushrooms are examples of fungi. They, like animals, do 

 not possess the power of photosynthesis. 



71. Algae. — It is believed that all the other groups of 

 plants evolved from forms like algae. The lowest of the 

 algae show us the simplest kind of plant life. They are 

 evidently of much scientific importance. It is from forms 

 like the simplest algae that the higher plants evolved. The 

 larger and more complex algae, such as grow in salt water, 

 also evolved from simple algae, but are believed not to 

 have given rise to forms more complex than themselves. 

 The great majority of algae are water plants; they grow 

 either in the water or where water is abundant. 



Some of the marine ■ algae (seaweeds) are of much 

 economic importance. They are much used in Japan for 

 food. In France seaweeds are collected for the ex- 

 traction from them of iodine. Recently, our own govern- 

 ment has begun the collection of seaweeds in the Pacific 

 to use them as a source of potassium for fertilizers. 

 The structure of land plants appears to be largely de- 

 termined by the need to protect against loss of water, 



