176 ECOLOGY 



Describe the characteristics of each group, giving atten- 

 tion to all the vegetative parts of the plant body. 



B. In woods or thickets make lists of the sun plants and shade plants, 

 and classify the trees roughly as regards their tolerance of shade con- 

 ditions. Measure the relative illumination of some of the plants which 

 live in the deepest shade by the method given in Exp. XXVIII. 



C. Study the distribution of plants as related to the character of the 

 soil, looking for species characteristic of limestone and of sandy soils. 

 If possible, find assemblages of plants in loose sand, especially of sand 

 dunes, and report on their peculiar form and habits. If there are 

 accessible localities for halophytes, examine the vegetation of salt 

 marshes, of the sea beach, or of " alkali " lands, and describe some of 

 the most noticeable characteristics of these plants. 



D. Examine and report on any epiphytes that may be found. 



References. Clements, 59 ; Warming-Groom-Balfour, 57 ; Pound and 

 Clements, 58. 



158. Laboratory study of ecological classes.** Make a sketch of at least 

 one typical member of each of the three principal ecological classes as based 

 on water requirements. Make careful studies of any available material and 

 discuss as many as possible of the following topics : 



A. Relative importance of the root system in aquatic plants. 



B. Special provisions for photosynthesis, respiration, and circulation of 

 air in the plant body of aquatic plants. 



C. Comparison of the structure of the leaves of deciduous trees, broad- 

 leaved evergreens (such as holly, live oak, and some rhododendrons), 

 and needle-leaved evergreens. In this study pay especial attention to 

 the total area of the three kinds of leaves, to their relative thickness, 

 to the thickness of the cuticle and the epidermis, and to the protection 

 of stomata by their position at the bottom of grooves or pits in the 

 epidermis. 



D. Appearance of plants in their resting condition (during winter's cold 

 or summer's drought) in any available bulbous- or tuberous-rooted 

 species or in fleshy-rooted biennials (e.g. parsnips, beets, or carrots). 



E. Characteristics of plants slightly, moderately, and decidedly xero- 

 phytic, as illustrated by wild plants of the neighborhood or (if these 

 are not obtainable) by such species as Euphorbia spleiidens, houseleek, 

 Echeveria, and cactuses. 



F. Difference in the appearance of a species grown in dry soil, with 

 leaves exposed to warm, dry air, and that grown in damp soil under a 



