THE VITAL PHENOMENA OF THE CELL 



221 



" Suitably prepared longitudinal and transverse sections of the 

 growing-points of roots and shoots show characteristic cell-wall 

 networks and cell arrangements, which agree with the type, even 

 in the most various plants. This depends essentially upon the 

 fact that the embryonic substance of the growing- point, as it 

 increases in volume on every side and at all parts, becomes divided 

 up into compartments or chambers by cell-walls, which intersect 

 one another at right angles. The longitudinal section of a growing- 

 point always shows a system of periclinal walls, intersected by 

 anticlinal walls, which in their turn represent the right-angled 

 trajectories of the former. If only the growing-points of flat 

 structures be considered, then there will be only two systems of 

 cell-walls present ; if, however, the growing-point is hemispherical 

 or conical, or of some other similar shape, that is to say not flat, but 

 forming a solid mass, a third system of cell-walls must be taken 

 into account ; namely, the longitudinal walls, which stretch out in 

 a radial direction from the longitudinal axis of the growing-point." 



" It will facilitate a clear comprehension of the subject, if 

 before proceeding farther we examine a diagram, which has been 

 constructed arbitrarily, although according to fixed laws, and 



p J 1 P P x J> 



Fig. 111. Diagram of the cell arrangement at a growing-point. (After Sachs, Fig. 281.) 



for this purpose it will be well to consider as a starting-point a 

 median longitudinal section through the growing-point (Fig. 111). 

 Confining our attention, therefore, to our figure, of which the out- 

 line E E represents the longitudinal section through a conical 

 growing-point which resembles fairly closely those met with in 

 nature it will be seen that it has the form of a parabola and 



