BIOLOGY OF HIGHER SEED PLANTS 13 



d. Summarize the relation of the following factors in the 

 development of the conical form and the false whorls 

 in the spruce and pine: 



(1) The number and position of the buds that grow 



each season. 



(2) The spiral plan of the pine and the spruce, and its 



relation to the false whorls of branches. 



(3) The effects of pruning. Consult the text (pp. 19 



and 20) on the development of the pine. 



THE AMERICAN ELM 



Select a terminal shoot of an elm representing three or four 

 years of growth, and observe the following points, as in the 

 pine and spruce just studied : 



1. The plan and development of an elm branch. 

 a. Leaves and buds. 



(1) Compare the leaf and bud arrangement on the elm 



branch with that of the lilac, ragweed, and spruce. 

 Are the leaves and buds in the elm arranged like 

 those of any one of the plants thus far studied ? 

 Is the leaf arrangement favorable to the maximum 

 exposure to light ? Observe an entire elm branch 

 from above. Observe the leaf petioles. Do they 

 curve so as to bring all of the leaves in one 

 plane ? Observe the buds. Is there a true ter- 

 minal bud or is it subtemiinal, that is, just below 

 the apex of the shoot ? 



(2) Sketch a single terminal twig of the elm to illus- 



trate the arrangement of buds and leaves and the 

 light relation of the leaves. Label parts carefully. 

 1. Seasonal growth of buds and branches. 



(1) Determine the age of the main axis and of the 

 lateral branches by means of bud-scale scars. 



