118 PHYSIOLOGICAL PROCESSES IN PLANTS 



trip. Look especially on the leaves of such plants as the water lily. Are 

 they on the upper or lower side of the leaves ? 



Conclusions. 1. Is a stem of spongy tissue well or poorly adapted to 

 permit air from the water to reach its interior ? 



2. What advantage in the stomata being on the upper side of a leaf ? 



Observation. Pull up one of the rooted plants. How do they differ 

 from any near-by land plant ? How do the roots of each differ ? 



Conclusion. What seem to be the main functions of the roots of 

 such water plants ? 



b. Xerophyte Society 



Observations. (Study such plants as the cactus, rubber plant, and 

 century plant. If none are growing wild, visit greenhouses.) 

 1* What is the character of the soil, sand, rock, or clay, etc.? 



2. Find water content as under mesophytes (meadow). 



3. What plants do you find ? Which are the most abundant ? 



4. Pull up some of the plants and examine the roots, if growing wild. 

 How do they compare with those of mesophytes ? Hydrophytes ? 



Conclusion. Why do these plants need long roots ? 



Observations. 1. Do all of these plants have leaves ? If so, how do 

 they compare in thickness and width with mesophytic plants ? Hydro- 

 phytic ? 



Conclusions. 1. Why should xerophy tic plants either be leafless, or 

 with leaves usually thick and fleshy ? 



2. If no leaves are present, what is the character of the stem ? 



c. Mesophyte Society 



1. MEADOW 



Observations. 1. Collect a sample of the soil in a pint fruit jar. 

 Bring it to the laboratory and get the weight of the sample. Then dry 

 the sample thoroughly, using slow heat. What is the weight of the soil 

 water in your sample ? What is the percentage of water (water content) 

 in the meadow soil ? 



2. Get the names of all the plants growing here that you can. Are 

 they few or abundant ? 



3. Pull up a few of the plants and note their roots. How do they dif- 

 fer from those of the hydrophytes ? Do you find root hairs ? 



Conclusions. 1. Can you think of any reason why the roots of 

 meadow mesophytes should be better developed than those of hydro- 

 phytes ? 



