Be 
stained by hæmatoxyline (fig. 174 A). Trichocytes may occur. The greater part of 
the crust is polystromatic, being composed of vertical cell-rows, up to 8 cells high 
or more. The older parts of the crusts are very irregular, being composed of several 
smaller crusts or lobes growing partly over each other. These partial fronds or 
lobes are usually polystro- 
matic to the very margin. 
The compound crusts may 
be composed of lobes of 
the same frond or of dif- 
ferent fronds growing to- 
gether; it is therefore im- 
possible to state the dia- 
meter of the single frond. 
In the thicker fronds, the 
upper ordinary frond-cell 
may bear more than one 
cortical cell, frequently one 
over the other (fig. 174 A, D). 
In the last-named figure the 
three undermost cells at 
right bear each a cortical 
cell, the i explanation of 
which must be that they 
represent the monostroma- 
tic border of the frond, 
which has been overgrown 
by tissue produced by the 
neighbouring thicker part 
of the same frond. A si 
milar process often takes 
Fig. 174. place in various parts of 
Melobesia trichostoma. Å, vertical section of the monostromatic part of a the frond and gives rise to 
frond growing over the conceptacle of another frond of the same species. : 
B, monostromatic frond seen from above. C, vertical section of older, com- the complicated structure 
pound crust. D, vertical section of a thick lobe of frond. E, vertical section of the old crusis, new lobes 
of sporangial conceptacle. C, 65:1, the rest 350 :1. 
developing from certain 
parts of the frond, and growing over the neighbouring parts. — The length of the 
cells of the vertical cell-rows is highly variable, usually one to three times as long 
as the breadth, and irregularly varying in the same filament. The undermost cell- 
layer is not distinct from the others, its cells being of variable height. The cells 
contain often numerous starch-grains. Transversal pores between the cells of different 
cell-filaments never occur, but transversal fusions are frequently met with, between 
the cells of the basal layer and between cells of the upper parts of the vertical 
cell-rows as well (figs. 174, 175). 
