82 OUTLINES OF PLANT LIFE. 



sudden changes ; or it may be composed mainly of mechan- 

 ical tissues, and be fully exposed, as are the shoots of trees. 

 In these cases the leaves generally perish and drop off an- 

 nually, but in the "evergreen" plants they live more than 

 one growing season. 



EXERCISE XVII. 



Shoots Examine the shoots of the linden, elm, maple, oak, and lilac 



and observe the mode of branching, and the arrangement of the buds. 



Study the construction of winter buds of lilac, horsechestnut, or hick- 

 ory. (This can be done most easily by examining them just as buds are 

 unfolding in spring, or by keeping shoots in a warm room for a few days, 

 when the buds will begin to open.) Observe the form and arrangement 

 of the scales and the way in which foliage leaves are folded. How are 

 these buds protected against water ? Against sudden changes of temper- 

 ature? (1187,133.) 



Examine the rhizomes of couch grass, mint, Solomon's seal or blood- 

 root; the bulb of the onion or hyacinth; the tuber of the white potato, 

 as forms of underground storage shoots (Tf 93, 98). Do these shoots 

 have buds on them ? 



Examine the tendrils of the passion flower (or the wild cucumber vine) ; 

 the thorns of the haws or the honey locust, as special leafless forms of the 

 shoot. 



102. Summary. — The shoot grows at the tip, new lateral 

 members being formed in regular succession below it. These 

 young members and the tender tip itself, protected by some 

 older leaves, compose the terminal bud. Similar growing 

 points arise on the sides of the main shoot and exist for a 

 time as lateral buds. Some buds die, and some live but re- 

 main undeveloped. Others develop into branches similar to 

 or different from the main axis. Special forms of the shoot 

 are produced to serve special purposes, such as storage, 

 reproduction, protection, climbing, etc. The branches, 

 some or all, and even the main shoot, die after a time. An- 

 nual shoots die after one growing season, biennial shoots 

 after two, and perennial shoots after several or many. 



