TYPES OF STEMS, 37 1 



721. The climbing type. The grapes, clematis, some roses, 

 the ivies, trumpet creeper, the climbing bittersweet, etc., are 

 climbing stems. Like the prostrate type, the climbers economize 

 in the material for stem building. They climb over shrubs, 

 up the trunks of trees and often reach to a great height and 

 acquire the power of displaying a great amount of foliage by 

 sending branches out on the limbs of the trees, sometimes devel- 

 oping an amount of foliage sufficient to cover and nearly smother 

 the foliage of large trees; while the main stem of the vine may 

 be not over two inches in diameter and the trunk of the supporting 

 tree may be three feet in diameter. 



722. Floating stems. These are necessarily found in aquatic 

 plants. The stems may be ascending or horizontal. The 

 stems are usually not very large, nor very strong, since the water 

 bears them up. The plants may grow in shallow water, or in 

 water 10-12 feet or more deep, but the leaves are usually formed 

 at or near the surface of the water in order to bring them near 

 the light. Various species of Potamogeton, Myriophyllum, and 

 other plants common along the shores of lakes, in ponds, slug- 

 gish streams, etc., are examples. Among the algae are exam- 

 ples like Chara, Nitella, etc., in fresh water; Sargassum, Macro- 

 cystis, etc., in the ocean. In these plants, however, the plant 

 body is a thallus, which is divided into stem-like (caulidium) and 

 leaf-like (phyllidium) structures. 



723. The burrowing type, or rhizomes. These are horizon- 

 tal, subterranean stems. The bracken fern, sensitive fern, the 

 mandrake (see fig. 4130), Solomon's seal, Trillium, Dentaria, 

 and the like, are examples. The subterranean habit affords 

 them protection from the cold, the wind, and from injury by 

 certain animals. Many of these stems act as reservoirs for the 

 storage of food material to be used in the rapid growth of the 

 short-lived aerial shoot. In the ferns mentioned, the subterra- 

 nean is the only shoot, and this bears scale leaves which are 

 devoid of chlorophyll, and foliage leaves which are larger, and 

 the only 'member of the plant body which is aerial. The foliage 

 leaf has assumed the function of the aerial shoot. The latter i? 



