L.VBOKATOEY AND FIELD EXEK< ISES 



(2) Xerophytic habitats. Does it occupy exposed dry 



cliffs and hillsides, sandy regions, or mountain 

 sides without adequate water supply ? Is it 

 found in marshes or swamps which are physio- 

 logically dry on account of the condition <>f the 

 bog water ? 



(3) Hydrophytic habitat. Does the species live in soil 



flooded or saturated with water ? 



b. Geographical habitat and <K*tnb*tion. Determine the 

 natural habitat and distribution of the species on 

 the American continent by means of manuals and 

 maps. Consult maps and descriptions in Hough's 

 " Handbook of North American Trees " if this work 

 is available. Consult the text, Fig. 223, and the 

 discussion of trees and shrubs. 

 2. Habit. 



a. Is the species being studied mesophytic, xerophytic, 



hydrophytic, or tropophytic in habit ? 



b. Size and form. Is it large or small as compared with 



other trees in the region ? Is it erect or spreading in 

 habit ? Is there a single excurreut trunk or does the 

 trunk divide above into two or more secondary axes ? 



c. Body plan and development. Review the text discus- 



sion in Part I on the development of trees and its 

 relation to body plan, bud growth, and pruning in 

 the spruce and elm. See Fig. 11 of text. 



d. Study the relation of the following four main factors, 



which determine the form of a tree, to the ultimate 

 form assumed by the species you are observing, as 

 indicated below: 



(1) Body plan. Is the species you are studying cyclic 

 or spiral in leaf and bud arrangement ? If spiral, 

 is the phyllotaxy J, f , f , or a higher fraction ? 



