146 MORPHOLOGY OF TISSUES. 



case also the ultimate separation of the mass of tissue into two distinct portions 

 is determined by the first divisions of the youngest segments ; but a comparison of 

 the corresponding process in the stem of Equiseium shows that the mass of tissue 

 which is formed from the central portions of the sextant has quite a different 

 signification from what it has there ; and the same is the case with the peripheral 

 layer. A further discussion of the origin of the forms of tissue of the root out of 

 these portions of the primary meristem will be entered into when treating of Ferns 

 and Equisetacese. 



In conclusion, it may be remarked that the segments of the apical cell, where 

 they arise in two or three rows, have at first a position oblique to the ideal axis of 

 the organ, and enclose an angle open towards the apical cell ; but, in consequence 

 of growth, the position of the segments generally changes so that they come to lie 

 gradually more transversely, and finally, at a certain distance from the apical cell, 

 the principal walls lie at right angles to the axis of the organ. The process is not 

 clearly shown in Figs, in and 112; but more evidently in examples to be brought 

 forward later {e.g. Fig. 116, p. 153). 



(b) Growing Point without an Apical Cell. This occurs universally in Phanero- 

 gams ; the apical region of growing shoots, leaves, and roots consisting of a primary 

 meristem, the cells of which are very small in proportion to the size of the entire 

 growing point, and very numerous. It has not yet been demonstrated whether 

 even the cells next the apex can be traced back to a single primary mother- 

 cell, although sometimes undoubtedly one cell lying at the apex is distinguished 

 by a somewhat greater size and by its form. In many shoots the surface of the 

 apex seen from above shows an arrangement of the superficial rows of cells 

 which to a certain extent points to this one cell as their common primary mother- 

 cell; but even if this were the case, which is by no means proved, it is, on the 

 other hand, altogether impossible to connect genetically the inner layers of cells 

 also with this cell. The peculiar significance of the apical cell of Cryptogams lies 

 in the fact that all the cells of the primary meristem furnish evidence of descent 

 from it in diff"erent degrees. 



But as in Cryptogams the first divisions of the segment-cells determine certain 

 layers of the primary meristem which subsequently pass into the differentiated tissue- 

 systems further backwards from the apex, so also in Phanerogams a definite 

 arrangement of the cells is brought about in the primary meristem of the growing 

 point, of such a kind that the various layers of the primary meristem, when 

 followed further backwards, have a genetic relation with the epidermal tissue, the 

 cortex, and the fibro-vascular bundles, and may be recognised as the first rudiments 

 of them. The outermost layers run uninterruptedly over the apex of the growing 

 point, overarching an inner mass of tissue of the primary meristem, which latter, 

 on its part, sometimes runs out beneath the apex into a single cell (in Hippuris 

 and Anacharis canadensis, according to Sanio), but usually terminates in a somewhat 

 subordinate group of cells. 



While in Cryptogams with an apical cell an evident cell of this kind is formed 

 where a lateral outgrowth (shoot, leaf, or root) is about to be developed on the 

 growing point, in Phanerogams, on the other hand, a whole group of cells, 

 including inner and outer layers, makes its appearance at the spot in question, so 



