30 Plants and their Ways in Sonth Africa 



the root-tip, until it reaches the bundles of long slender tubes 

 that pass from the roots through the stem to the very tips of 

 the leaves. The tubes are not continuous through the length 

 of the plant, but the water passes from one tube to another 

 adjacent one. After this water has brought the minerals to 



the place they are re- 

 quired, part of it passes 

 out through the leaves 

 and stems into the air. 

 This escape of water is 

 called transpiration, 

 or sometimes perspira- 

 tion. Some of the 

 water is used to make 

 food for the plant. 



The water, in its 

 long journey, must not 

 be dried up, and to 

 guard against this, under 

 the thin green dress of 

 stems and branches an 

 undergarment of cork is 

 found. This garment is 

 made of small cells also, 

 but while the cells beneath have spaces between them to admit 

 the air, cork cells fit closely together, and the walls are water- 

 proof; so cork in trees serves the same purpose that it does 

 in bottles. The cork cells are filled with air, and these air 

 spaces, like the loft in a house, keep the tree cool in summer 

 and warm in winter. 



As the tree grows, the thin green over-dress gets too small ; 

 sap cannot get to it through the cork, so the cells of \Yhich it 

 is made starve for lack of food ; it cracks and peels off, and 

 the tree henceforth is clothed in more fitting shades of grey or 

 brown as become its years. Young cork cells stretch, but in 

 time they lose their elasticity and become too small also. Just 

 underneath lie special cells which keep it renewed, so that the 

 tree is always properly clothed. Difterent trees fashion their 



Fig. 36. — G, central cylindL-r, consisting of pith, 

 vascular bimdles, and pericj'cle ; A', cortex ; 

 E piliferous layer ; W, root-cap. (From Ed- 

 monds and Rlarloth's " Elementary Botany for 

 South Africa.") 



