136 Proceedings of the Royal Society of Edinburgh. [Sess* 
1. It is invariably terminal, being normally found at the end of a very 
short branch. 
2. It is more robust than the preceding and has thicker walls (Plate, 
fig. 2 ; Plate, fig. 4). 
3. It is invariably solitary. 
The size varies from 30/* to 45/* (text-fig. 3 c ) ; the wall appears to con- 
sist of two layers, but it was not found possible to establish this fact with 
certainty. In the matured form the wall is invariably ruptured (Plate, fig. 4), 
the cleft being typically roughly quadrangular in form and situated opposite 
Fig. 3. 
to the point of attachment of the vesicle to the stalk. Another example is 
shown in text-fig. 3. Among modern Phycomycetes this type is common ; 
we find it in the swarm-sporangia of Peronospora and Phytophthora among 
the Peronosporacese, and in Py thium among the Saprolegniacese. There can 
be little doubt that the fossilised spheres are the remains of swarm-sporangia 
of P. gracilis. Whilst other explanations are not precluded, the uniformity 
in the size, shape, and position of the cleft seems to indicate that this cleft 
was caused by the breaking out through the membrane of the contents of 
the sporangium. The fossil structures differ in one very important feature 
from their modern representatives, namely, in the total absence of a 
separating wall between the sporangium and the hyphal stalk on which it 
is borne. This seems to indicate a more primitive form of reproduction 
than prevails among the related structures of modern fungi. 
