96 General Botany 



tinguished as groups because of their great difference of habitat 

 and appearance. But it is not always easy to decide whether a 

 particular plant is a xerophyte, hydrophyte, or mesophyte, be- 

 cause we find all gradations of form among plants of the three 

 classes. Nevertheless, these terms are useful in describing the 

 water relations of most plants. 



PROBLEMS 



1. Why do plants that are wilted in the late afternoon of a hot summer day recover 



their firmness during the night, even though there is no rain ? 



2. Where, near your home, do mesophytes, xerophytes, and hydrophytes occur? 



3. In what regions of the United States are mesophytes most common? 



4. In what parts of the United States are xerophytes abundant? 



5. In what parts of the United States are hydrophytes common? W^hat states 



have very few hydrophytes ? 



6. What xerophytes furnish useful products to man and animals? 



7. Are there any economic plants that are hydrophytes? 



