655 
on species of Tolypothrix. 
of the algal vegetation in the lower of the two Pen Ponds, 
Richmond Park, last November ; since then the Alga has 
practically disappeared. 
In the material collected in November, 1902, all the algal 
filaments presented a healthy appearance, and the only indi- 
cation of the presence of the Fungus was to be found in the 
occurrence of numbers of colourless spores of relatively large 
size between the threads of the Tolypothrix . These spores 
had rather thin walls generally differentiated into two layers, 
and possessed clear, homogeneous contents (Fig. 1) ; many of 
them had grown out at one or more points, giving rise to 
unseptate hyphae, which frequently followed the course of the 
algal filaments externally, not rarely enveloping them in 
a perfect mycelial web, which, however, remained purely epi- 
phytic. In germination the external layer of the membrane 
is ruptured, and the contents surrounded by the internal 
layer grow out. One curious feature observed at this date 
remains to be mentioned. Some of the spores appeared 
to lie within the external layer of the Tolypothrix- sheath, 
a position for which I am unable to account (Fig. 1). 
In samples of the same Alga, collected a month later, it was 
at once apparent that some change had taken place. In 
many places the dark green colour of the Tolypothrix had 
given way to a dirty greenish-yellow, and all transitions 
between these two colours could be observed with the naked 
eye. A microscopic examination showed that now, in addition 
to the abundant epiphytic mycelium of the Fungus, large 
numbers of hyphae had penetrated into the interior of the 
Alga 1 ; Fig. 2 shows a germinating spore, the hypha from 
which has pierced the sheath and grown for a short distance 
inside the host. Once successfully inside, the Fungus makes 
rapid progress, and large numbers of the algal filaments were 
found to contain long moniliform hyphae, like the one shown 
1 It is curious that a diligent search revealed no traces of parasitic hyphae a 
month before. Possibly the Fungus is only able to penetrate into the Alga, when 
the latter is in a low state of vitality. The way in which the filaments of the latter 
are enveloped by the epiphytic mycelium might alone tend to produce such a state ; 
and thus ultimately make it possible for some hyphae to penetrate into the host. 
