138 



THE SCIENCE OF LIFE. 



the stem, the other the root ; the growing part of both 



being bathed in the cambium fluid. 



In the growing stem the 

 terminal cells (a. Fig. 57, 

 A) multiply and enlarge, 

 while they furnish new 

 cells to the cambium layer. 

 In the root, however, the 

 multiplying cells are not 

 quite at the extremity. A 

 sort of cap is formed by 

 the growing cells, (pileor- 

 hiza^) and receives addi- 

 tions to its interior, which 

 push out the layers exter- 

 nal to them. (Fig. 57, B, 

 C.) Thus efficient protec- 

 tion is afforded to the new- 



FIG. 57. A. Mode of growth in stem. B. In - , 



root. A. a. Growing cells in stem, which ly-tormed tlSSUC. 

 multiply by fission, b. Cambium, elaborated 

 by growing cells. B. a. Growing cells in 



root. b. Cells produced by growing cells. Q f the tisSUCS of 3. 

 c. Cap, (pileorhiza.) C. Root of duckweed, 



(magnified.) . Growing point, b. Root- ing plant may be seen in 



sheath, c. Cap. d. Root. . 



Fig. 58. Air passages are 



both intercellular and vascular, the latter in Exogens 

 being dotted ducts and spiral vessels. The bark con- 

 tains elongated liber or bast cells, but there are no sca- 

 lariform vessels as in Acrogens. The chlorophyll (Chap. 

 VI, Sec. 2) is found chiefly in the cells immediately un- 

 der the epidermis. See also Figs. 15 and 16. The roots 

 are supplied with water containing carbonic acid, air, 

 and oxygen, in addition to the minerals and decompos- 



crf-rif^r^ 1 a rra n cr^m (*n r 



