THE ARCHEGONIATJE 



209 



destroyed as the spores mature, and they then lie free in the venter of the 

 archegonium, which has kept pace with the growth of the embryo and has 

 become two-layered. 



FIG. 167. Targionia hypophylla. A, longitudinal section of the thallus, showing 

 the archegonia, ar, and ventral scales, I, I (X 100). B, section through a pore, 

 showing the chlorophyllous cells, cl, in the air-chamber (X 300). 



Suborder II. Corsiniaceae 



This is a small group intermediate in character between the Ricciaceae and 

 the Marchantiacese. There are no species found within the United States. They 

 differ from the Ricciacese in having the lower part of the embryo developed into 

 a foot, and some of the archesporial cells remain sterile, and form rudimentary 

 elaters. There are two genera, Corsinia and Funicularia (Boschia). 



Suborder III. The Marchantiaceae 



The Marchantiaceae, with the exception of the aberrant genera Dumortiera 

 and Monoclea, have the assimilative tissue of the thallus sharply differentiated 



