264 



BRYOPHYTA 



B. THE JUNGERMANNIALES. 



The same principle is illustrated also in the Jungermanniales, but with 

 differences of detail. In these the first segmentation of the zygote 

 separates a hypobasal cell, which in some cases develops as a multicellular 



FIG. 124. 



Frullania dilatata, development of the embryo. X 300. (After Leitgeb). x, x^ the 

 archesporial cells. The numbers indicate the primary transverse divisions. (From 

 Campbell, Mosses and Ferns.) 



haustorium (Frullanid), but more frequently remains as a minute appendage 

 at the base of the fruit, while the epibasal cell gives rise to the capsule, 

 stalk, and foot. So far as a comparison on the basis of the segmentation 

 of the zygote is valid, this would indicate in the Jungermanniales a still 



further delegation of function from the 

 hypobasal to the epibasal half of the 

 embryo. 



The epibasal half of the zygote under- 

 goes segmentation, so that a number of 

 transverse discs are formed, each composed 

 of four cells, while the terminal tier is 

 composed of four octants of a hemisphere 

 (Fig. 124). The segmentation is often 

 very regular, but exceptions exist. 1 The 

 FIG. 125. uppermost tier of cells appears to be cut 



Embryos of Radula compianata. X2 3 o. off by the first transverse wall in the 



(After Leitgeb.) 7, 8, show the basal ap- ., . , , r r , , . 



pendage cut off b y the first segmentation of epibasal half of the zygote, and in many 



the zygote : a shows the upper region of a c i i T 



more advanced embryo. of the Anakrogynous Jungermanniaceae 



the whole of the capsule is derived from 



these cells : subsequent intercalary divisions in the lower half of the 

 epibasal cell gave rise to the sterile seta. But, on the other hand, in many 

 of the Akrogynous Jungermanniaceae for instance, in Radula it is shown 

 by Leitgeb 2 that some of the lower tiers of cells also take part in the 

 formation of the capsule ; in Radula the number of these appears to be 

 three (Fig. 125). Thus there is in such cases no general distinction, on 



1 See Campbell's Figs, of Porella ; Mosses and Ferns, Fig. 55. 



2 Lebennoose, ii., p. 55. 



