Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 245 
the chambers may not have originated from splits 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 glauca L. Fics. 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 Fic. 6, immediately above 
the apical cell the meristematic tissue forms a compact mass 
Fic. 6. Longitudinal section through a growing point, X 500.’ x, apical cell. 
Fic. 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. 
