Rhabdonia tenera , J . Ag. 41 1 
Structure of Mature Cystocarp. 
The cystocarps are immersed in the frond, which they 
cause to swell out on one side in a striking manner. A cross- 
section of the frond passing through the centre of the cysto- 
carp shows that just outside the latter the cortex is thicker, 
and composed of smaller cells than it is elsewhere, and that 
an opening, the carpostome, leads from the outside to the 
cystocarp. The central part of the latter, commonly called 
the c placenta,’ is spherical in shape, and is composed of sterile 
cells which have no chromatophores. They are very irregular 
in size and shape. Surrounding this sterile mass is a spori- 
ferous layer composed of radiating filaments of spores from 
two to five cells in length, and often bearing two to four- 
celled branches. The sporiferous tissue is interrupted here 
and there by strands of elongated sterile cells proceeding from 
the f placenta ’ to a fairly thick pericarp, which surrounds the 
spores, and is composed of radiating filaments of cells which 
are smaller than those of the ‘ placenta 5 and elongated in the 
tangential direction. This elongation is especially marked in 
the outermost cells, which come to resemble the cells of the 
medulla with which they form secondary connexions by means 
of pits. 
The pericarp forms a complete investment to the cystocarp, 
except at the carpostome, and the application of reagents 
brings out the fact that it is enclosed in a special gelatinous 
envelope, which separates it from the medulla on which it 
abuts. 
In the older cystocarps spores are often found which divide 
irregularly and produce rhizoids, but their development is 
apparently soon arrested. 
Development of the Procarp. 
Procarps originate as a rule very close to the growing tips 
of the frond, but sometimes a few scattered procarps are 
formed in somewhat older portions of the plant, where the 
majority of the procarps are ready for fertilization. They 
