221 
Species of Olpidiopsis , (Cornu) Fischer. 
of development of the sexual spores of the three species agrees. There are, 
however, some slight differences, especially between O. vexans and the 
other two whose development resembles each other more closely. For the 
reason stated the former will be described separately. 
The developing sexual cells of O. vexans are first detected in the young 
stage by the darker and more dense appearing condition of the protoplasm 
of, especially, the larger, or female, cell. It does not require very high 
magnification to see that closely associated with the female plant are one 
or more smaller light-coloured protoplasmic bodies. These develop into the 
antheridia, while the larger become the oogonia. Such an early condition 
is shown in PL XXIV, Fig. 26. No walls have formed about the cells at 
this stage, and the very close association of the individuals might suggest 
a division of a single individual rather than the partial fusion of two or more. 
At this stage, were it not for the presence of the female cell, one could not 
distinguish the male elements from the young sporangia of the same age. 
As growth proceeds, the two cells become more and more distinct and 
soon surround themselves by cellulose walls, which become fused at the 
point of contact. Usually one can clearly distinguish what appear to be 
brace-walls joining the two cells, as seen in Fig. 27. The wall of the 
oogonium shows early the formation of roughenings on the outer surface, 
which eventually take on a warty appearance, and resemble an encrustation 
of some kind. The male cell, or antheridium, remains smooth. 
Noticeable changes also take place in the protoplasmic contents of both 
cells. In the young stages of growth these resemble those that take place 
in the young sporangia. There is at first in the oogonial cell a very much 
vacuolated, finely granular protoplasm in which a few larger irregular 
granules are distributed. Most of the protoplasm lies in a thin layer about 
the periphery, from which irregular strands extend into the interior. At 
this time the male cell shows a somewhat similar vacuolate condition, but 
contains more granular protoplasm. 
Following this stage, which, owing to rapid growth at this period, lasts 
but a short time, is a stage in which the number of large granules have 
greatly increased in both cells, to such an extent as to make difficult the 
observation of protoplasmic changes within, especially in the oogonium. 
Soon the contents of the female cell become more or less clumped, while 
that of the male shows a fine granular condition with frequently one or more 
vacuoles. The cells are now ready for fertilization. 
This takes place by the passage of all the antheridial contents into the 
oogonium. The beginning of this phenomenon is indicated by the appear- 
ance of a large central vacuole or, as is more usual, a shrinkage of the 
protoplasm from the wall of the antheridium opposite the oogonium. The 
whole act may require several hours or may be completed in less than one 
hour. I have frequently observed long strands of protoplasm still clinging 
