652 Fritsch. — Two Fungi , parasitic 
were marked by the formation of a group of the thick-walled 
spores, abutting directly on the heterocyst. 
These spores arise in the following way : a single segment 
of the Fungus increases somewhat in size and acquires a 
thicker wall. This is followed by the appearance of one or 
two large oily granules in its homogeneous contents (Fig. 27). 
Ultimately the wall differentiates into two layers and acquires 
a dark brown colour, and the number of oily granules present 
generally increases (Figs. 20, 26). The spores have very 
much the same shape as the fungal segment, from which they 
arise ; generally a slight rounding-off takes place in their 
formation. These thick-walled cells are of the nature of 
chlamydospores ; ultimately the remainder of the Fungus 
disappears and they alone remain, lying within the empty 
algal sheath (Fig. 22). They probably undergo a long period 
of quiescence before germination takes place. 
Occasionally hyphae are formed as branches on the parasitic 
mycelium, which emerge from the Alga into the surrounding 
medium (Fig. 25). They are generally very delicate and 
show no trace of septation, although drops of oily matter, 
which to some extent simulate partition-walls, frequently 
occur in their course. I have no doubt that they serve to 
infect other (healthy) algal filaments, although I have been 
unable to obtain figures of such cases. 
Except for the absence of zoospore-formation, the Fungus 
I have just described is in most essentials similar to the 
Resticularia nodosa of Dangeard. The latter observer con- 
siders the thick-walled spores 1 to have arisen by a sexual 
process ; he remarks (Dangeard, ’ 90 , p. 98) : ‘ La reproduction 
sexuelle se fait de la maniere suivante : sur le trajet d’un 
meme filament le protoplasma se condense par place comme 
le montrent les figures 29 et 30 ; on ne saurait faire aucune 
distinction entre le protoplasma male et le protoplasma fe- 
melle, bien qu’il y ait souvent l’une des portions un peu plus 
grosse que la seconde ; le filament mycelien sur lequel se 
forment ces zygospores ne parait pas se cloisonner ; du moins, 
1 Dangeard does not remark that the walls of the spores take on a brown colour. 
