INTBOOUCnOM 5 



region, nearly or quite destitute of a lamina, and upright brand** which 

 grow from the rhizome. In these upright shoots, the lamina is broadly 

 expanded and repeatedly forked. These dichotomously branched snoots 

 resemble very closely the leaves of certain small (ems. especially the 

 menophyllaceae (Fig. i, A). 



Of the three species to be discussed in the present paper, two. P. iWi- 

 culosa and /' belong to the section Eupallavicinia. the third. P. 



ZoUingeri, to Mittcnia. 



The general structure of the thallus is much the tame in all 

 r rhizome-like portion occurring in some specks, the 

 is differentiated into a very distinct midrib, several cclU thick, and a defa- 



lamina, or wing, on each side of the nu<lrit>. these marginal wingt 

 being always in Eupallavicinia but a single cell in thickness; hot in Mine- 



hey merge more or less gradually into the midrib. The midrib it 

 traversed throughout its extent by a strand of conducting tissue composed 

 of cr narrowed and greatly elongated, pointed at the ends. 



an.l with thick pitted walls. 



Branching is of two types. In the first there is an apparent 



the equal branches having th Ss and "yfwtiq 



tinuous with those <>f t shoot The second type of 



has the appearance, superficially, of exogenous adventitioai 



ing on the ventral surface of the midrib. In these ventral 

 the conducting tissue is not connected with the midrib of the mai 

 (Fig. 2, /f. B). 



Rhizoids occur more or less abundantly on the lower turf ace of the 

 thallus where it is in contact with the substratum 



ic species are dioecious, the reproductive organs being borne 

 upon the dorsal surface of the thallus. The antheridia, which are pro- 



! by Males, occur either upon the midrib or close to it. The 

 gonia are in definite groups which are surrounded by a double 

 the outer one forming th< the inner envelope a more or less 



tubular sheath, the "tKTianth " 





