mer is terns of Ferns as a Phylogenetic Study . 331 
mode of branching passes over by imperceptible gradations 
from the monopodial to the dichotomous, the branchings 
approaching successively nearer and nearer to the extreme 
apex. It is thus to be clearly understood that, though in 
Trichomanes rctdicans the ultimate branchings of the frond 
are of the dichotomous type, the earlier branchings are 
monopodial, and that the transition is to be seen in the 
individual frond, as is the case in other leptosporangiate 
Ferns. Further, though no sharp limit can be drawn between 
the two, it is to be noted that the monopodial branching is 
characteristic of that part of the frond where a wedge-shaped 
apical cell is present, while the dichotomous branching is 
characteristic rather of that part where T division is found at 
the extreme apex ; the pinnae, however, which have at no 
time a wedge-shaped apical cell, branch monopodially in 
their lower parts : the state of matters in Trichomanes radicans 
seems accordingly to be this : — (1) that dichotomous branching 
occurs only where T division is found at the apex ; (2) that 
where a wedge-shaped apical cell is present only monopodial 
branching takes place. 
The mode of development of the wings will be described 
later (see p. 342). 
Observations were also made on Trichomanes reniforme , 
as being a most markedly different species as regards the 
character of the leaf : here as before a wedge-shaped apical 
cell, and marginal series were found, but the identity of the 
apical cell is lost at a comparatively early period, by the 
appearance in it of a T division (Fig. 33) ; since there are no 
pinnae formed in this species it is difficult to draw a com- 
parison between the period when this division takes place and 
the disappearance of the apical cell in Trichomanes radicans. 
Such observations as I have made on Hymenophyltnm 
Tunbridgense fall in with those on Trichomanes , and putting 
these together with the observations of Prantl, it may be 
concluded that a two-sided wedge-shaped apical cell is 
constantly present at the apex of the young leaf of the 
Hymenophyllaceae, and that a series of cells derived in the 
