46 COMPENDIUM OF GENERAL BOTANY. 



A cell-surface is a cell-complex formed of a single layer of cells, 

 whose septa are approximately vertical to the surface of the cell- 

 complex, but may form any :mgle relative to each other. Ex- 

 amples: some algae, moss-leaves. 



A cell-body is a cell-complex in which the cells are placed side 

 by side in three directions. 



A cell-lilament is formed from a single cell. This may take 

 place (1) by the exclusive division of an cqyical cell (Fig. 26 I), or 

 (2) by the combination of intercalary division with apical cell- 

 division (26 II). In Fig. 26 II a apex and base are wanting ; the 

 cells of the filament are of nearly equal dimensions. In Fig. 26 

 II }) there is a definite apical cell in which would appear the fifth 

 septum. 



A cell-surface may arise from a single cell (Fig. 27 la and 16) 

 or from a cell-thread (27 II a and Wlj). Cell-division may be 

 wholly peripheral in that only the marginal cells divide (Fig. 27 II h 

 represents an older segment of a cell-filament in which this fact is 

 indicated), or the internal and marginal cells divide (27 II « and I J, 

 final stage). 



A cell-body may develop from a cell, a cell-filament, or a cell- 

 surface. As soon as cell-walls in a cell appear in three different 

 directions we have a cell-body. Here also we may consider the 

 division of inner and outer cells independently of each other. We 

 shall proceed at once to consider one of the most important growth- 

 types of a cell-body. 



A. Stem-structure among Yascular Cryptogams and Mosses 

 (Fig. 28 «, &, c). — Among Equisetacecs, and many ferns, as well as 

 among some leafy mosses, there is found at the apical area of the 

 stem a three-sided pyramidal (tetrahedral) cell, called the "apical 

 cell." This cell divides, forming successive spirally arranged septa. 

 Fig. 28 a presents a lateral view, 28 J a surface view from above 

 ('' apical view "). In many instances, for example, in the " bilateral " 

 stem of Selaginella^ the apical cell is approximately " two-edgedo" 

 An apical view is shown in Fig. 28 (? ; a lateral view is similar to 

 Fig. 28 a. 



Since all the cells of such an organ can be traced to the segments 

 of the apical cell, and thus to the apical cell itself, we may with 

 propriety speak of a single vegetative point. 



B. Boot-structure of Vascular Cryptogams (Fig. 29). — The 

 tetrahedral apical cell not only forms successive spiral segments, 



