458 



LECTURE XXVII. 



volume of the successive segments, and from the number of partition-walls in 

 segments of different ages. 



So far as regards the importance of the apical cell as the ruler of the whole 

 growth in the growing-point, however, I showed that that cell represents merely 

 a break in the constructive system of the growing-point-^i. e. the apical cell 

 is that spot in the embryonic tissue in which neither anticlines and periclines nor 

 radial longitudinal walls have as yet been formed. In order to understand this, 

 it is only necessary to compare Fig. 295 with the previous scheme, Fig. 289. 

 There, a few of the periclines run continuously round the focus beneath the apex, 

 and in the same way the uppermost region of the apex is traversed by anticlines, 

 so that the proper apical region of the growing-point is occupied by small areolae or 

 cells. In Fig. 295 ^, which possesses an apical cell, the periclines all cease, on the 

 contrary, at some distance from the apex ; we need' only complete these, however, 

 into confocal parabolas with the focus S, and suppose in addition a few sharply 

 curved confocal and parabolic antichnes interpolated above the uppermost anticline 

 A, and then the impression of an apical cell disappears altogether, and we have a 

 growing-point such as is found in all Phanerogams and many Cryptogams. Or, 

 conversely, we need only suppose in our scheme. Fig. 289, the anticlines next the 

 apex and the upper curved portions of the periclines to be wanting, and we obtain 

 an apical cell, as in Fig. 295 A. In apical cells from which segments are cut off 

 on two or three sides, the relation referred to is, it is true, a little more complicated, 

 but it is easily noticed on regarding Fig. 295 B that here also we are enabled by 

 properly completing the periclines P, with the help of a few anticlines, to convert the 

 apical cell into a small-celled mass of tissue. As a matter of fact, corresponding 

 transformations of apical cells actually occur when the growing-points cease to grow 

 further as such, e.g. in the prothaUia of some Ferns. 



By means of this explanation of the apical cell which I have established, the 

 criticism of the constructive processes in the growing-point obtains as a general 

 principle. While growing-points with and without apical cells were previously 

 regarded as essentially different, and the opinion was even entertained that an 

 apical cell must be found even in all phanerogamous growing-points; according 

 to my view of the matter, on the contrary, the presence or absence of an 

 apical cell appears as an interesting but quite secondary point in the growth of the 

 growing-point. Even the case as it occurs, for example, in the roots of the Marattiacese 

 among the Ferns, where a group of large apical cells is present, may be 

 referred without constraint to the principle mentioned. It is to be mentioned on 

 the other hand that apical cells are only possible, in the sense here employed, when 

 the periclines and anticlines constitute systems of confocal curves, or, shortly, 

 in growing-points with confocal structure. If, on the contrary, the growing-point 

 is traversed by anticlines which run in a fan-like manner, and the increase in 

 volume is greatest towards the apex, as was shown above in Fig. 288, it is then 

 possible, under certain circumstances, still to assume the existence of apical cells 

 in the wider sense, but in these cases authors have not spoken of apical cells, and 

 so we also may overlook them. In any case, in the older mode of looking at the 

 apical cell, it must remain enigmatical why this varies so extraordinarily in its 

 occurrence and even in its form that, as it was formerly expressed, the growth of 



