On an Endophytic Parasite of Diatoms. By G. Ilaugliton Gill. 3 
The very high authority of Zopf as a cryptogamic botanist, gives 
the greatest possible weight to his opinion that the sacs which he 
observed were really the mycelial sacs of some species of Ancylista 
(a parasitic fungus), but as he too failed to get any growth from 
them or their contents, their exact nature is still open to some degree 
of doubt. 
It is, indeed, hard to understand how it should come about that a 
fungus which was present in such abundance, and in such an active 
state as to attack thousands of individuals of Pleurosigma, should not 
invade one of the almost equally numerous Nitschise , Pinnularise, or 
other diatoms which were confined in the same limited volume of 
water for weeks together. But such was the case. No trace of 
a mycelium from which such spore-sacs might arise could be 
discovered. 
The first gathering in which these bodies were observed (and I 
had been examining similar gatherings from the same spot, at short 
intervals throughout the spring and summer) was made in the 
beginning of November. It was kept in an open shallow dish and 
examined daily. At first only one or two specimens could be 
found even after long search, but in the course of a week or two 
examples became more numerous, among those diatoms which were 
still left alive. In the beginning of December many specimens could 
be found in each “dip,” but by the middle of the month the greater 
number of the sacs had put forth their beaks and discharged their 
contents. 
A fresh gathering was made from the same spot on Dec. 19. On 
examination no Pleurosigma with fully-formed sacs could be found. 
It was kept in an open dish and examined every few days, but it was 
not till the 2nd January that complete spore-sacs were observed. 
From this time the number rapidly increased up to the 22nd of the 
month, and then as rapidly decreased, till by the 31st there were 
hardly any but discharged and empty sacs to be found.* 
A third gathering made at the beginning of March, and kept 
under the same conditions as the other two, failed to give any 
specimens of Pleurosigma in this peculiar state. 
All through the succeeding spring and summer these sac-bearing 
Pleurosigma were sought — but not one specimen found. So far 
their occurrence appears to be seasonal. 
In October of this year (1892) I again found a few specimens, 
but up to the beginning of November only very few, and even in 
December they are scarce as compared with last year. The fact that 
in no case have more than a few scattered specimens been found in 
quite fresh-gathered (and therefore presumably healthy) material, but 
* Observations made in November and December 1892 and January 1893, have 
completely coincided with those ot' the previous year. Now, at the end of January, 
1 am unable to fiud one Plentosiqma with a spore-sac. 
B 2 
