116 PHYSIOLOGICAL PROCESSES IN PLANTS 



13. Why are male fertilizing cells so much smaller than eggs ? 



Note. Water plants set sperm and eggs free in the water, where 

 fertilization takes place and the resulting spore (seed) usually sinks to 

 the bottom to germinate when conditions are right. 



14. Why must mosses, ferns, etc., protect their eggs until and after 

 fertilization ? How is this accomplished ? 



Special Reports 



1. The advantages and disadvantages of alternation of generations. 



2. Means of overcoming unfavorable conditions of development. 



3. The importance of protecting the egg. 



4. Ways in which sperm cells reach the egg. 



5. The main differences between algae and fungi. 



References 



Hunter, Essentials of Biology. Chap. XI. 

 Leavitt, Outlines of Botany. 480-484. 



PROBLEM XXI (Optional) 



A study of the way plants are modified by their sur- 

 roundings. (A field trip.) 



INTRODUCTION 



Note. Most plants must have soil, water, light, air, and proper tem- 

 perature in order to grow. Plants use these factors in different propor- 

 tions, so are organized into groups or societies, which express their 

 relations to these different factors. As the relation or reaction to water 

 is perhaps as evident and universal as any, it is commonly used as the 

 basis of grouping. Thus there are : 



a. Hydrophytes, or water plants, or groups. 



b. Xerophytes, or those in sandy, rocky, or other dry places. 



c. Mesophytes, or those intermediate between water plants and those 

 of dry regions. 



Other divisions may be also made on a temperature or on a soil basis. 

 The above societies may be further subdivided into swamp society, pond 

 society, rock society, sand society, meadow society, thicket society, prairie 

 society, forest society, etc., or they may take their names from the 

 most conspicuous plant present, as an oak, cactus, or water lily society. 



