84 



Fo^somhronia or some of the larger species of Dendroceros. 

 The midrib is broad and strongly concave above, so that in 

 transverse section (PL X5 Fig. 59) it appears crescent shape. The 

 "leaves" are broadly expanded and lobed and folded in a very 

 complicated fashion. None of the prothallia of this species were 

 found that equalled in size the large specimens of G. dichotoma, 

 and few specimens were found showing a dichotomy of the apex. 



The arrangement of the reproductive organs is not alwa3^s 

 the same. In all of the species examined, exept G. laevujata 

 where no young prothallia were found, it is evident that 

 autheridia are formed first in the young prothallia, where very 

 few archegonia had been developed (PI. IX, Figs 38 — 40). There 

 are numerous antheridia, many of which are old ones, and in all 

 of these the antheridia are found on the under surface of the 

 thin wings and also upon the sides of the thickened midrib, 

 or even in some cases among the archegonia. The latter are 

 first developed upon the slightly enlarged cushion at the for- 

 ward end of the midrib, just as they occur in most other ferns; 

 but in the older prothallia especially, they are often restricted 

 to the sides of the midrib and resemble in this respect Osinunda, 

 with which the prothallia have other points in common. 



In G. laevigata (PI. X, Fig. 59) the position of the antheridia is 

 quite different from that of the other species. The archegonia 

 are mainly confined to the sides of the very broad midrib, 

 but the antheridia are usually borne upon the lateral leaf-like 

 lobes and may occur on the upper or lower side. They may also 

 be developed upon the upper surface of the midrib. Autheridia 

 of very different ages are found together, showiug that their 

 development is not strictly acropetal. 



The apical growth of the prothallium is very much like that 

 of other ferns. The apex, seen in horizontal section (PI. X, Fig. 60), 

 shows a row of marginal cells (./) of which one is usually 

 larger than the other and probably represents a single apical 

 cell, although this is not absolutely certain as the divisions in 

 the neighboring apical cells are similar. The lougitudiual section 

 of the thallus presents an appearance of the apex entirely 



