48 



COMPENDIUM OF GENERAL BOTANY. 



C. The Lichen-Type. — A collection of cell-filaments form a cell- 

 body with an apical cone similar to the ones just mentioned. The 

 filaments lying immediately about the axis in which growth pro- 

 ceeds divide continuously. Those lying some distance from the 

 axis of growth seldom branch. In this form of growth any given 

 point not lying at the apex moves forward in an " orthogonal 

 trajectory " until the cell-body has acquired its definitive width. 



The following question is important as pertaining to the sub- 

 ject under discussion in this chapter. 



How is a tissue of similar, that is, of equally large, cells con- 

 verted into a tissue of unequally large cells ? Three methods will 

 be mentioned as being especially important : (1) inequality in the 

 length of the cell- wall formation of contiguous cells (see Fig. 30, A) \ 

 (2) unequal growth of contiguous cells (Fig. 31) ; with this condition 

 is very closely allied the so-called gliding groivth, a phenomenon of 

 which Krabbe has recently made a special study ; (3) division in 

 cells of equal growth may cease at different periods of time. The 

 elongated cells in Fig. 30, B^ are formed in this manner. 



X I 



Fig. 30. 



Fig. 31. 



While the formation of stems and roots among mosses and in 

 the majority of vascular cryptogams is quite accurately known and 

 studied, and proceeds approximately in the manner indicated, the 

 facts regarding corresponding organs in phanerogams are not so 

 well known. Only in a few cases was it possible to demonstrate 

 definitely, or approximately, the presence of a "single apical area." 

 For example, four apical cells arranged in a quadrant about the axial 

 line were observed in stems of Coniferoe (Schwendener). Other 

 observations (Dingler, Korschelt) speak for a single apical cell. 

 The diflficulty of making the investigations explains the contradic- 

 tory statements. Johannes Hanstein in his time (about 1868) 

 sought to demonstrate the existence of a special growth-type in 

 phanerogams. He taught that there was a special formative tissue 

 for the epidermis, the parenchyma, and for the central tissue of 



