STEUCTUKE A^J) WOKK OF PLANTS 



11 



available to the plant, the outgo from the leaves is often 

 greater than the income from the roots, and in such cases 

 wilting follows. If water does not again become available, 

 the plant will die, but with a renewed supply turgidity and 

 the resulting rigidity soon return. 



11. Stems and their work: water passes through the stem. 

 The stem is a means of connection between the roots and the 

 leaves. It also serves to support the leaves in the air. Ascend- 

 ing water passes mainly through special regions of the stem 

 and the leaf. When a fresh leaf of celery or leafy stem of 

 hydrangea is placed for a few minutes in one of the ani- 

 line dyes, and then removed and examined 1 )y sectionurg, defi- 

 nitely stained regions appear, which show not only that the 

 staining liquid passed upward into the stalk, but that it passed , 

 through only certain tissues of the stalk. These special tissues 

 through \\luch the liquids pass are composed of bundles of 

 very small tubular cells which are many times as long as they 

 are thick. The bundles are known as fihrovaHcuJar InouJles, 

 — which term simply means " collections of thread-like tubes." 

 The different cells of these bundles o^'erlap one another in 

 such a way that they are continuous from roots, through stem 

 and branches, into the lea\-es. In the leaves the bundles are 

 the so-called veins 

 (Fig. 7). 



12. Stems and 

 their work: kinds 

 of stems. There is 

 a striking and im- 

 portant difference 

 in the arrange- 

 ment of fibroxas- 

 cular bundles in 

 the stems of different kinds of plants. If a stem of corn or a 

 plantain leafstalk is broken, whitish strings are pulled from 

 the pith (Fig. 8). These are vascular bundles. They are 

 somewhat irregularly distributed throughout the stem, and 



Fig. 8. A cornstalk broken so as to show the number 

 and distribution of the vascular bundles 



