138 



PRACTICAL COURSE IN BOTANY 



FIG. 158. Winter spray 

 of elm. 



angle, for instance, which a twig makes with its bough has a 

 great effect in shaping the contour of the tree. Compare in 



this respect the elm and hackberry; 

 the tulip tree and willow ; ash and hick- 

 ory. As a general thing, acute angles 

 produce slender, flowing effects; right 

 or obtuse angles, more bold and rugged 

 outlines. 



Practical Questions 



1. Has the arrangement of leaves on a twig 

 anything to do with the way a tree is branched? 

 (145, 151,152.) 



2. Why do most large trees tend to assume 

 the excurrent, or axial, mode of growth if let 

 alone? (150, 154.) 



3. If you wished to alter the mode of growth, or to produce what nur- 

 serymen call a low-headed tree, how would you prune it? (152, 153.) 



4. Would you top a timber tree? (152, 153.) 



5. Are low-headed or tall trees best for an orchard ? Why ? 



6. Why is the growth of annuals generally indefinite ? 



7. Name some trees of your neighborhood that are conspicuous for 

 their graceful winter spray. 



8. Name some that are characterized by sharpness and boldness of outline. 



9. Account for the peculiarities in each case. 



II. BUDS 



MATERIAL. Expanding leaf and flower buds in different stages of 

 development ; large ones show the parts best and should be used where 

 attainable. Some good examples for the opposite arrangement are 

 horse-chestnut, maple, lilac, ash; for the alternate: hickory, sweet gum, 

 balsam poplar, beech, elm. Where material is scarce, the twigs used in the 

 last section may be placed in water and kept till the buds begin to expand. 



155. Folding of the leaves. Remove the scales from a 

 bud of horse-chestnut nearly ready to open, and notice the 

 manner in which the young leaves are folded. This is called 

 vernation, or prefoliation, words meaning respectively " spring 

 condition " and " condition preceding the leaf." Leaves 

 are packed in the bud so as to occupy the least space possible, 

 and in different plants they will be found folded in a great 



