THE APICAL CELL. 



453 



important fact in 1845, showed how all the tissue-cells, not only of the growing- 

 point but also all those subsequently produced by their agency, may be compre- 

 hended as descendants, with definite sequence in space and time, from the segments 

 of one apical cell. For more than thirty years the most careful investigations 

 have been devoted to this study, and for this reason alone it is necessary for 

 us to concern ourselves here somewhat more closely with it, and especially 

 because serious errors with respect to the relations between growth and cell-division 



Fig. 290.— Apex of a shoot of CAar«— longitudinal sectii 



have slipped into the subject — errors which have retarded the development of the 

 whole doctrine of growth. In the first place, however, it is necessary to make the 

 reader acquainted with the facts. 



When an algal filament or a fungus-hypha grows in length, this takes place 

 usually, but by no means always (e. g. not in the case of Spirogyra and other Con- 

 jugatae), in such a manner that transverse divisions are formed only at the end of the 

 filament which represents the growing-point. The cell at the end, which alone grows 

 forward and divides, may be distinguished as the apical cell : such a cell is also found 

 at the end of the rhizoids of Mosses and Characese, where, however, the transverse 



