in Rhodymeniales : II. Delesseriaceae . 1 8 1 
able modification of parts, though each is still capable of 
identification with the earlier condition already described. 
First, the filaments, other than the carpogonial branch, derived 
from the same pericentral cell with it, which, when no fertiliza- 
tion takes place, help to form the thickened midrib, now take 
on a characteristic appearance. These filaments are two in 
number ; one, the larger, springing laterally, and the other, 
smaller, posteriorly (Figs. 12 and 13). In all, the tuft which 
these filaments constitute consists of a score or so of cells. 
When fertilization of a procarp takes place, these cease to 
grow further, although all the adjacent filaments in a similar 
situation take on a more active growth. The cell-walls 
become greatly thickened and highly refractive, and sharply 
contrast on this account with the rest of the tissue. The 
neighbouring filaments growing more vigorously, soon arch 
over and bury them, without however completely closing the 
aperture above. The gap thus left is the apical pore of the 
future cystocarp (Fig. 16). A small portion of the external 
surface is thus covered in, and may still be distinguished by 
the foreign substances adhering to it. Both these changes, 
that in the tuft of filaments which cease to grow, and that 
in the adjacent filaments which grow the more vigorously, 
indicate beyond doubt on which side of the thallus fertilization 
has taken place. I have never found these changes taking 
place on both sides the thallus, or at more than one spot on 
the thallus. As it is unlikely that only one procarp becomes 
fertilized on a branch, it is probable that the demand for 
nutrition consequent upon the occurrence of the first act of 
fertilization prevents the formation of a second cystocarp. The 
case is analogous with that of the ovule of Pinus , for example, 
where of many possible embryos only one normally matures. 
To turn however to the carpogonial branch and the peri- 
central cell from which it is derived. At the stage above 
described it is still possible to distinguish the cells of the 
carpogonial branch, especially since they form a characteristic 
filament owing to the inequality in the size of the successive 
cells. The cells, however, have by this time greatly altered 
