34-8 Davis . — On the Development of the Frond of 
sections were cut serially on a Minot microtome *01 mm. 
in thickness. There was no cell-shrinkage, when care was 
taken not to let the paraffin get too hot, but with large 
specimens there was always danger of the hollow frond 
collapsing. 
Transverse sections of the young plants will first be con- 
sidered, for it is these alone that show how the group of 
initial cells arises. The smallest plant sectioned was ‘io mm. 
long, and there were ten sections in the series. Eight of these 
sections are shown in Fig. io, in the order in which they 
were cut. This plant was more advanced than that shown 
in Fig. 6, although it was not so long. Its base was disc- 
shaped, and was not raised on four organs of attachment, as 
the case figured in Fig 9. 
The first section, Fig. 10 a, shows the four initial cells at 
the apex of the frond, arranged in the form of a cross. They 
are numbered j , 2, 3, 4, and appear also in the second section, 
Fig. 10 t?. The four initial cells are the same as the four 
cap-cells of the segmented spore. They have divided several 
times, giving rise to daughter-cells behind them, and are now 
smaller than they were at first. 
The other sections are very interesting, because there is an 
apparent division of each section into four parts. In the 
stained specimen this division was very noticeable, much more 
so than can be represented in outline-drawings, for the older 
cell-walls between the four divisions stained much more 
heavily. I have drawn in each figure two straight lines to mark 
the extent of the four divisions. It will be remembered that 
in the later stages of the segmentation of the spore there were 
always present four clearly marked divisions, each of which had 
a cap- cell at the top, and at the bottom was terminated by an 
organ of attachment. It is interesting to find this division into 
four parts present for so long a time in the young plants. 
Fig. 11 shows the first two sections from another slide of a 
plant *15 mm. long, and Fig. 12 is the first section of a plant 
•17 mm. long. In both of these plants the four initial cells 
derived from the four cap-cells are distinct. They are num- 
