92 MR. C. B. PLOWRIGHT ON CERTAIN 
This Puccinia differed from P. Scheleriana in its smaller sori and 
in its uredo-sori causing much less discoloration of the affected 
leaves. Specimens of the Puccinia were carefully preserved 
during the winter under such conditions as I had previously 
found most likely to ensure free germination in the following 
spring*. Towards the end of March (1885), the Puccinia-spores 
began to germinate; and on 81st March a number of freely 
germinating spores were placed upon the unfolded leaves of a 
plant of Centaurea nigra. lt was not until the 21st April, how- 
ever, that the ZEcidium showed unequivocal signs of its appear- 
ance. This long period of incubation on the part of the parasite 
is quite in accordance with my previous experience of cultures 
made during the colder seasons of the year. The next culture 
was on the 8th April, when nine separate plants of Centaurea 
were infected with the Puccinia, on all of which the Zeidium 
had begun to appear in ten days. Similar cultures were made 
on 12th May, 1885, and 24th May, 1886, all of which were 
followed by the same result. 
The converse cultures, of placing the scidiospores from the 
Centaurea on Carex arenaria, were made on the 12th and 15th of 
May, and were equally successful, the Uredo appearing on the 29th 
May and 6th June respectively. In due course the Uredo was 
followed by the Puccinia. Further, these pucciniospores of 1885 
again gave origin to the ZEcidiwm in 1886. It was, however, further 
necessary to establish the distinction of Puccinia arenariicola from 
ihe other two British Carez-affecting Puccinie—P. Caricis and 
(especially) P. Scheleriana, the latter occurring on C. arenaria. 
With this object several duplicated cultures were made in the 
following manner :—A quantity of the spores of P. arenariicola 
were germinated in a watch-glass, one half of which were placed 
on a plant of Centaurea nigra, and the other half on a plant of 
Senecio Jacobea: the former gave rise to the ZEcidium, the latter 
did not. A converse duplicated culture was, in the same man- 
ner, made with the spores of P. Scheleriana, one half of which 
were placed on Senecio Jacobea and the other half on Centaurea 
nigra: theformer gave rise to the ZEcidium, the latter did not. 
Similar duplicated cultures were made with P. arenariicola on 
Urtica dioica and Centaurea nigra: the latter was successful, and 
* For the benefit of those botanists who are interested in this subject, I 
purpose at an early date to give a detailed account of the modus operandi of 
performing these uredine cultures. 
