128 PRACTICAL COURSE IN BOTANY 



5. Which is the better for timber, a tree grown in the open, or one 

 grown in a forest, and why? (Plate 7.) 



6. What are the objects to be attained in pruning timber trees? Or- 

 chard and ornamental trees ? 



7. Is the outer bark of any use to a tree, and if so, what ? 



8. Why should pruning not be done in wet weather? [140 (3), 141.] 



9. Why should vertical shoots be cut off obliquely? [133, 140 (3), 

 141.] 



Field Work 



(1) Make a study of the various climbing plants of your neighborhood 

 with reference to their modes of ascent, and the effect, injurious, or other, 

 upon the plants to which they attach themselves. Note the origin and 

 position of tendrils, and try to make out what modification has taken 

 place in each case. Consider the twining habit in reference to parasitism, 

 especially in the case of soft-stemmed twiners when brought into contact 

 with soft-stemmed annuals. Observe the various habits of stem growth: 

 prostrate, declined, ascending, etc., and decide what adaptation to cir- 

 cumstances may have influenced each case. 



(2) Notice the shape of the different stems met with, and learn to 

 recognize the forms peculiar to certain of the great families. Observe 

 the various appliances for defense and protection with which they are 

 provided, and try to find out the meaning of the numerous grooves, ridges, 

 hairs, prickles, and secretions that are found on stems. Always be on the 

 alert for modifications, and learn to recognize a stem under any disguise, 

 whether thorn, tendril, foliage, water holder, rootstock, or tuber. 



(3) Note the color and texture of the bark of the different trees you see 

 and learn to distinguish the most important kinds : 



(a) scaly peeling off annually in large plates, as sycamore, shagbark- 



hickory ; 

 (6) fibrous detached in stiff threads and fibers, as grape ; 



(c) fissured split into large, irregular cracks by the growth of the 



stem in thickness, as oak, chestnut, and most of our large forest 

 trees ; 



(d) membranous separating in dry films and ribbons, as common 



birch (Betula alba). 



Observe the difference in texture and appearance of the bark on old 

 and young boughs of the same species. Try to account for the varying 

 thickness of the bark on different trees and on different parts of the same 

 tree. Notice the difference in the timber of the same species when grown 

 in different soils, at different ages of the tree, and in healthy and weakly 

 specimens. Find examples of self-pruning trees (Plate 7), and explain 

 how the pruning was brought about, 



