42 STEMS AND BUDS 



shoots increase in length for a few weeks only and the remainder 

 of the season is used for matnring the wood and bnds. Such 

 growths are not likely to winter-kill, and the growths of succes- 

 sive years can be readily traced by the bud scars on the stem. 

 The shoots of other plants grow throughout the entire season and 

 until checked by the cold weather ; they are known as iridefinite 

 growths, and are likely to suffer from winter injury. The roses, 

 lilacs, sumac and ailanthus or tree-of-heaven are excellent ex- 

 amples of this type of gTowi;h. 



Underground stems produce buds at the nodes in the same 

 manner as the stems above ground. The so-called " eyes " of 

 the potatoes are buds which give rise to shoots. The bulbs of 

 many plants, although usually described as stems, are, in 

 reality, buds. 



EXERCISES WITH STEMS AND BUDS 



1. Study of Woody Twigs. — Cut a branch from a maple, linden, horse 

 chestnut or other dicotyledonous tree and note the nodes and internodes 

 of the newest growth as marked by buds and scales ; trace as many seasons 

 of growth as possible, beginning with the tip of the twig. Examine the 

 bark with a hand lens and note leaf scars, lenticles and other peculiarities. 



2. Monocotyledonous Stems. — Examine a corn stalk, grass stem, 

 grain straw and other monocotyledonous stems and compare with a woody 

 stem studied in previous exercise. 



■'>. Cross-section of Herbaceous Stem. — Cut through a Begonia stem 

 (dicotyledonous), examine with a hand lens and note (a) the central mass 

 or pith surroiuided by (b) a circle of wedge-shaped areas which are fibro- 

 vascular bundles of wood, and which are separated from each other by 

 material like the pith and known as medulkiry rays. Outside the fibro- 

 vascular bundles is another zone which is in turn surrounded by the 

 epidermis or harJ: covering. 



4. Layers of Bark. — ^Take the last season's growth of a lilac, horse- 

 chestnut or maple. Gently scrape oil the outer brown bark, the inner 

 green bark and the fibrous bark and examine with a hand lens and note, 

 (a) the outer bro\\TX baik layer, (b) the second or dark green layer of 

 new bark and (c) the third layer of tough fibrous bark or bast. 



.'>. Cross-section of Woody Twigs. — Cut through a woody twig of 

 oak or basswoful and note (a) tlie central pith surrounded bj^ (b) the 



