Evans: Air chambers of Grimaldia fragrans 245 



the chambers may not have originated from spUts between super- 

 ficial cells, as Deutsch and Miss O'Keeffe maintain is the case in 

 Targionia. 



The thallus of Grimaldia fragrans is so complex that it is 

 impracticable to trace the cell divisions which take place in the 

 segments cut off from the apical cell, as Pietsch has so ably done 

 in the case of Riccia glanca L. Figs. 6-8, however, give some idea 

 of the apical region and bring out the fact that a single apical cell 

 with four cutting faces is present. In Fig. 6, immediately above 

 the apical cell the meristematic tissue forms a compact mass 



FiG.~6. Longitudinal section through a growing point, X 500. x, apical cell. 

 Fig. 7. Longitudinal section through another growing point, X 500. x, apical cell. 



without intercellular spaces. Between the fourth and fifth cells 

 the first indication of a chamber appears in the form of a split a 

 short distance below the surface. Between the fifth and sixth cells 

 an older and longer chamber is visible, which has reached the 

 surface, apparently through the upward extension of a similar 

 split. The elongation and widening of the chamber have been 

 largely due, it would appear, to the growth of the bounding cells. 

 The still older chambers shown in the figure are not cut squarely 

 in the middle and need not be further considered. 



