280 



METAMORPHOSIS 



are fully developed. The form of the apical cell is, however, still identical 

 with, or at least very like, that of Stypocaulon. At the ends of the stems of 

 mosses and ferns we meet with another form of apical cell, distinguished by 

 being two- or three-sided. In the latter case it has the form of a tetrahedron 

 or a three-sided pyramid with its curved base facing outwards. Cell divisions 

 take place parallel to the three surfaces which face inwards and follow each other 

 in definite order, so that the individual segments which are cut off from the 

 three-sided pyramid are arranged in three rows behind the apical cell. Very soon, 

 however, further division-planes divide these up into a large number of cells. 



The stem-apex of the Phanerogam is more complicated still. Here we find 

 no predominant apical cell to which all the other cells may be referred ; the 

 apex consists, on the other hand, of a group of many cells. Fig. 76 shows the 

 conical growing point of an aquatic plant as seen in longitudinal section. An 

 axial cellular strand (pi) stretches backwards and is surrounded by four envelop- 

 ing layers of cells (pr], whose outlines almost converge into five confocal para- 

 bolas. These parabolas are traversed by a number of parabolas cutting them 

 at right angles, which have the same focus and the same axis, but which are 



d 



f Fig. 76. Longitudinal section through the 

 growing point of Hippuris wulgaris. f, leaf 

 primordia. From the Bonn Textbook. 



Fig. 77. Diagram of the arrangement of cell- 

 layers in the growing point. After SACHS (1878). 



laid out in the opposite direction. The orthogonal trajectories of the first- 

 mentioned parabolas are not so apparent because they are often interrupted ; 

 still they are seen in SACHS'S schematic figure (Fig. 77) as complete curves. We 

 will confine any further remarks we have to make to this figure, thereby defi- 

 nitely affirming that the small differences between the diagram and what occurs 

 in nature are of no consequence so far as the correctness of our exposition is 

 concerned. In the diagrammatic longitudinal section we note rows of cells 

 which appear like bent cell filaments ; those which run almost parallel with 

 the outer surface, and indicated in the figure by the Roman numerals 1 -VI 

 we term periclines, those crossing them, 1-11, we term anticlines (SACHS, 1878). 

 In both periclines and anticlines the same phenomenon occurs, viz. that the 

 series with lower numbers are flatter, while those with higher numbers are always 

 more bent, until finally the highest numbers of all are curved round the apex and 

 the two arches touch each other in the line of the axis. In order to give some 

 conception of the probable mode of growth of a growing point of this kind, Fig. 78 

 shows on the left of the median line the upper portion only of Fig. 77 so far as the 

 anticlines 7-77 are concerned, while to the right the same five anticlines are repre- 

 sented at a later stage of development. It will be seen from this diagram that 



