4 Campbell . — Observations on the Development 
colour of the prothallium is much like that of Anthoceros , 
and also recalls strongly, as do the prothallia in other 
particulars, those of Osmunda cinnamomea. 
According to Jonkman, the prothallia of the Marattiaceae, 
like those of the other homosporous ferns that have been 
investigated, usually at least, grow by a two-sided apical cell 
which is afterward replaced by a group of marginal initials. 
In all the specimens at my disposal, the marginal group of 
cells was already formed and was often wider than is 
commonly the case in the Polypodiaceae. The form of these 
initial cells is much the same as in other ferns studied by me. 
When seen from above (Fig. i), they are more or less oblong 
in outline, but in vertical section (Fig. 3), they are nearly 
hemispherical. As usual, the basal segments are cut off by 
a wall that extends the whole depth of the prothallium, and 
the segment is then divided by a horizontal wall into a dorsal 
and ventral cell of nearly equal size. From the latter, the 
projecting cushion of tissue on the ventral side is formed. 
This arises abruptly by the multiplication of cells in the 
ventral segments some distance behind the apex. The 
superficial cells of the prothallium, especially upon the upper 
surface, have a strongly developed cuticle which makes it 
necessary to use a good deal of care in imbedding the pro- 
thallia for sectioning. Numerous root-hairs grow from the 
lower surface, especially from the midrib, and fasten the 
prothailium firmly to the ground. 
The sexual organs are found in large numbers upon the 
monoecious prothallia. The antheridia are formed first, and 
mainly upon the lower surface of the midrib, but also occur 
upon the upper surface of the prothallium. The archegonia 
appear later, and so far as my observations go, are confined 
entirely to the lower surface of the midrib. Upon the old 
prothallia they may be formed in great numbers, and as they 
turn dark brown when they fail to be fertilized, are readily 
visible to the naked eye as dark brown spots thickly studding 
the broad and thick midrib. Both antheridia and archegonia 
differ much from those of the leptosporangiate ferns, and the 
