410 THE NON-VASCULAR PLANTS 



the more it grows up into the light, the poorer are the 

 chances of its sperm to get to eggs on other plants ; what 

 is helpful to its leaf work is hurtful to its sperm work. In 

 mosses and liverworts we have leaf work done by the sperm- 

 bearing generation, but mosses and liverworts never be- 

 come tall ; they are lowly plants which are often covered by 

 enough moisture to permit the sperms to get from one plant 

 to another. Possibly mosses indicate just about the limits 

 of height to which it is possible for sperm-bearing stems to 

 ascend if the sperms are to' do their work ; they may be said 

 to represent the limits in the evolution of a leafy gameto- 

 phyte. Further evolution in the nutritive body of plants 

 was accomplished only by forms in which the nutritive 

 work was transferred to the spore-bearing generation, and 

 so was not limited in its development by having to conform 

 to conditions necessary to the movement of the sperms. 



QUESTIONS AND SUGGESTIONS 



Section 69. 1. What is meant by evolutionary sequence ? 

 2. What is meant by non- vascular plants ? Give three examples of 

 them other than those given in this section. 



Section 70. 1. Name the four great divisions of plants, and ex- 

 plain the meanings of these names. 2. State a principal difference 

 between algae and fungi, and give an example of each. 



Section 71. 1. Describe the places in which you have seen algae 

 growing. 2. In what ways are the needs of alga? as to structure 

 different from the needs of ordinary land plants ? 



A. 3. Describe Pleurococcus. 



B. 4. Describe Nostoc. 5. Describe Oscillatoria. 



C. 6. Describe the general structure of many-celled, fresh-water 

 algae. 7. Describe the reproduction of Ulothrix, defining cilia, gametes, 

 and oospore. 8. Distinguish between spores and gametes. 9. De- 

 scribe (Edogonium, defining oogonia and antheridia, and explaining 



