AS SEEN IN PTERIDOPHYTA 93 
margin. Fig. 47 illustrates how the series of cells of the archesporium 
is continuous both upwards and downwards beyond the limit of its fertility : 
this indicates a probability that its marginal limitation has been due to 
sterilisation, a view which is strengthened by comparison with Sphagnum 
(Fig. 48); for there the archesporium is in the form of a complete dome: 
Danaea elliptica, Smith. Drawings illustr 
A, tangential section through three sori, showi he loculi in ground plan: the septa are 
often thin, so that pairs of loculi are in close juxtaposition ; the loculi marked (+) 
are large, and show one or more partial septa. 20, 8, C, D, 4, show such loculi with 
partial septa in greater detail: in D and £ it is difficult to decide whether the cells 
marked (?) will develop as tapetum or as spore-mother-cells. x 150. 
partial septations of the sporangium. 
ual septat f th g 
a sterile condition of the cells at its apex would give a barrel-shaped 
archesporium, as is seen in the Bryineae. Thus it will appear that any 
evidence of sterilisation in the Musci is less direct than that in the 
Hepaticae. 
Evidence of sterilisation of potential sporogenous cells is common in 
the homosporous Pteridophyta: and, as in the Bryophytes, the function 
