DEVELOPMENT OF THE STEM. 



595 



in all directions, but subsequently in linear series ; the epidermal cells 



divide by horizontal and n 



parallel subdivisions; the 



cells of the intermediate cor- 



tical series, in the first in- 



stance, grow more after the ^ 



fashion of the central cells. 



When leaves or branches 



commence to be formed, the 



outer cells of the central 



mass divide by longitudinal 



partitions at the same time 



that the central mass itself 



exchanges its conical for a 



cylindrical form, ultimately 



constituting the medulla or 



pith. 



The form and position of 

 these gro wing-points depend 

 materially upon the form of 

 the primordial cells, and on 

 the direction (longitudinal, 



transverse, O1' oblique) of 



their partitions. The form 



i -i / i i n 



and mode of branching of 



the stern depend also, in a great degree, upon the position and arrangement 



of the buds. 



Fig. 600. 



Growing-point of Phaseolus (after Sachs). 



e first tw leaTC8; 



A, growing-point of Chara (after Sachs) : t, terminal cell, from which are formed a and 6, 

 which latter cells (nodal cells) are divided longitudinally, m. Below this is another 

 single cell (g) called an internodal cell. This is followed by mm, nodal cells. Each 

 cell is nucleated. The internodal cells (q) increase in length, but do not divide. The 

 nodal cells divide so as ultimately to envelop the internodal cells. From A the cell- 

 contents have been removed ; in B the protoplasmic and chlorophyll granules are seen. 



m Misled by certain appearances well calculated to produce a false impres- 

 sion, botanists at one time attributed the formation of woody matters in" 



