XIV 



ISOETACE^ 



547 



approaches more or less the vertical as the latter is more or less 

 inclined. Occasionally the basal wall is so nearly vertical that 

 the cotyledon grows upright and penetrates the neck of the 

 archegonium at right angles to its ordinary position. At the 

 base of the leaf at this stage a single cell, larger than its neigh- 

 bours, may often be seen (Fig. 315, A, I). This is the mother 

 cell of the ligule, found in all the leaves. This cell projects, 



D 



B 



Fig. 315. — Development of the embryo in I. echinospora var. Braunii. A, Median longi- 

 tudinal section: of a young embryo; B, four horizontal sections of a younger one; 

 C, two vertical transverse sections of an older embryo; /, the ligula, X300. 



and as the leaf grows divides regularly by walls in a manner 

 compared by Hofmeister to the divisions in the gemmae of 

 Marchantia. It finally forms a scale-like appendage about 

 twelve cells in length by as many in breadth. 



Almost coincident with the first appearance of the ligule 

 a depression is evident, which separates the bases of the cotyle- 

 don and root. The base of the latter, which now begins also to 



