84: Agricultural Chemistry. 



toward the center of the stem. Groups of these cells, which 

 traverse the pith of the stalk longitudinally, are familiarly known 

 as the fiber of hemp and the threads of the corn stalk. The 

 stems of exogenous plants like the oak and maple, which produce 

 new tissue outward from a compact, central heart- wood, consist 

 of a tough, supportive core of the older and denser tissue sur- 

 rounded by the growing cambium layer. This whole structure is 

 surrounded and protected by a layer of dead cells forming the 

 outer bark. Sap is conveyed about these plants through channels 

 in the cambium layer or inner bark, and may be obtained in 

 quantity from some trees, as from the sugar-maple, by tapping 

 into the inner bark and contiguous woody tissue in early spring, 

 when the rapidly developing buds are drawing upon reserve food 

 supplies in the trunk. In the case of the maple tree, starch and 

 other reserve carbohydrates are in process of transportation to 

 the buds in the form of sugars which may be recovered as such 

 by concentrating the sap. 



The stems of some plants have the appearance of roots fro: 

 the fact that they exist below the surface of the soil. The 

 of the peanut, for example, ripen in the ground because the flowe 

 stems lengthen and penetrate the soil as soon as the blossom falls. 



Root stocks or rhizomes are subterranean stems, each joint or 

 node of which puts out both leaf buds and roots. Each node is 

 thus equipped to become an independent plant as soon as it 

 isolated from the parent stem. It is to this fact that the e 

 treme troublesomeness of quack grass is due. Cultivation, e 

 cept in a favorable season of prolonged drought, serves to i 

 crease the pest. Asparagus is another example of a plant gro 

 ing from a rhizome and well illustrates the function of the ste 

 as a food magazine. 



Tubers are fleshy enlargements of the tips of subterrane 

 stems. Their ''eyes" mark the position of buds, which disti 

 guish them from true roots. Each of these eyes is the precu 

 of one or more new plants. The tubers of the potato, arro 

 root, and some other plants, are of great value as food beca 



