124 MORPHOLOGY OF TISSUES. 



seen by comparing the longitudinal section A with the transverse section B (c). 

 Here also three straight rows of segments are formed by successive divisions of the 

 apical cell, which are numbered according to their order in age, /, //, ///, &c., in 

 Fig. B ; and here also a spiral is described by the hne connecting the centres 

 of the consecutive segments. The great difference between the root and the apex 

 of the growing stem of Cryptogams lies however especially in this, that in the 

 former the apical cell not only produces these segments which build up the 

 tissue of the root ^ but other segments also which build up the root-cap. These 

 latter are cut off from the apical cell by septa in such a manner that they cover 

 them like a cap ; every such segment belonging to a root-cap is hence termed 

 simply a Cap-cell. According to the investigations of Nageli and Leitgeb, it 

 appears to be the rule that whenever three segments have been formed (from the 

 substance of the root), a new cap-cell arises; but this rule is not always strictly 

 adhered to. 



The cap-cell increases quickly in breadth, and its form, originally spherically- 

 triangular in transverse section, passes over into a circle. It is simultaneously 

 divided into two equal halves by a wall vertical to its original surface and hence 

 parallel to the axis of the root; in each of these halves a longitudinal wall again 

 springs up vertical to the former, by which four square cells are formed. Each 

 quadrant again breaks up into two cells (octants), the further divisions varying in 

 different species. In the layers of the cap which follow one another, the direction 

 of the quadrants is not the same but alternate ; i. e. the quadrant-walls of one layer 

 deviate from those of the preceding and following ones by about 45°. 



The growth in length of the substance of the root, in so far as it is occasioned 

 by divisions of the apical cell, proceeds, as has already been indicated, in such a 

 manner that the partition-walls which arise in spiral succession are parallel to the 

 sides of the apical cell. Each segment-cell is bounded by five walls, as at the apex 

 of the stem of Equisetum, — two principal triangular walls, two oblong side-walls, 

 and one somewhat convex outer wall, upon which lies a root-cap. The first w^all 

 which arises in each segment-cell stands at right angles to the principal walls, and 

 is, with reference to the whole root, a radial longitudinal wall. Two cells arise 

 in this manner lying close to one another, diff'ering in form and size, the partition- 

 wall meeting internally a side-wall, externally the centre of the outer wall. In this 

 manner the transverse section of the root, composed at first of three segment-cells, 

 breaks up into six cells or sextants (compare the processes described above in 

 the stem of Equisetum) ; three of these sextants reach to the centre of the section; 

 but the three which alternate with them do not. The sextant-walls are seen in 

 Fig. 102, B, in the segments IV, V, VJ, VII, as dividing lines of the outer wall; in 

 a transverse section made deeper they would form, together with the three side-walls 

 of the three segments, a six-rayed star, similar to that in Fig. loi, ^(compare 

 Book II, Equisetacege, diagram of root). Each sextant- wall is next divided again 

 by a wall parallel to the surface of the root into an inner and an outer cell ; in the 

 transverse section of the root at this stage {i. e. in the corresponding transverse 

 section beneath the apex), tw-elve cells can therefore be recognised, of which the six 



^ They are bounded by thicker lines in the longitudinal section A. 



