MORPHOLOGY 



149 



In the Common Horsetail (Equisetum arvense), for example, the apical 

 cell of the main axis viewed from above (Fig. 163, A), appears as an 

 equilateral triangle, in which new walls 

 are successively formed in a spiral direc- 

 tion, parallel to the original walls (p). 

 Each new segment thus derived is divided 

 by a new division wall (Figs. 162, 163, m) 

 into an upper and lower half ; each of 

 these halves, as is shown most clearly by 

 an optical section just below the apical 

 cell (Fig. 163, B), becomes again divided 

 by a sextant wall (s) into two new cells. 

 It is unnecessary to trace the further divi- Fro 

 sions, and it will suffice to call attention to 

 the fact, that all cell walls parallel to the 

 outer surface of such vegetative cones or 

 portions of plants are termed periclinal 

 walls, while such as meet the surface and 

 the periclinal walls at right angles are designated anticlinal, of 

 which those in the plane of the axis of an organ are called radial. 



161. — Diagrammatic representa- 

 tion of the apex of Metsgeria fur- 

 cota in process of branching, viewed 

 from the dorsal side, a, Apical 

 cell of parent shoot ; b, apical cell 

 of daughter shoot. (After Kny, 

 X circa 370.) 



Fig. 162. 



-Median longitudinal section of the vegetative cone of Equisetum arvense. 

 in the text. (X 240.) 



Explanation 



Some distance below the apical cell of Equisetum arvense the first leaf- 

 whorl arises from the vegetative cone as a circular wall, which grows by 

 the formation of cell walls inclined alternately inwards and outwards 



