STEMS 41 



The Work of Stems. — (i) The stems of trees, shrubs and 

 common herbs are mainly concerned in the conduction of 

 water and solutes from the soil, and of food materials. The 

 need for a conductive system first arose in the plant kingdom 

 when the food-making organs of the plant became elevated 

 above the soil or water surface. (2) The stem also is a 

 support to the other organs of the plant, and it brings into 

 display the leaves, and flowers. The leaves are brought 

 into a position where they may receive the light to advantage, 

 and flowers are placed where their pollen may be disseminated 

 by wind or bees, and seeds may be more easily spread. (3) 

 In addition to conduction and support, stems may store 

 food material, water and various waste products. In our 

 woody perennials, such as the apple or peach, for example, 

 an abundance of food material is stored during the winter 

 in the medullary ray cells, also, in wood parenchyma, and in 

 that portion of the pith adjacent to wood, and sometimes 

 in all of the pith cells; portions of the phloem, and cortex 

 may also store food. The stems of such plants as the giant 

 cactus, and other cacti, store large quantities of water. 

 Some stems, such as the potato tuber, bulb, corm and root- 

 stock, are heavily loaded with stored food material. (4) 

 Young stems that contain chlorophyll in their outer layers 

 possess the power of manufacturing carbohydrates, just as 

 do green leaves. 



