CERTAIN BRITISH HETERCECISMAL UREDINES. 
159 
that of Uromyces pose occurs rather earlier in the year than 
that of P. Magnusiana. 
Puccinia phragmitis gave rise to no iEcidium on Ranun- 
culus repens (137, 138), nor on R. ficaria (142), although 
the teleutospores were in active germination when employed. 
But the subject is not even yet fully exhausted. The emi- 
nent Danish botanist, Mr. P. Nielsen, in 1879, 1 found that the 
iEcidium onRumex acetosa was developed from P. phrag- 
mitis, and Winter 2 gives his adherence to this view. Now, 
Mr. Nielsen is a most careful and expert experimenter with 
the Urediues. I therefore performed the following experi- 
ment. A quantity of P. phragmitis was placed in water in 
a watch-glass, when it was found, by microscopical examination, 
that the spores were in active germination ; one half was 
placed on a plant of Rumex acetosa (347), and the other 
half upon one of R. obtusifolius (346). The infected plants 
were both treated alike, but while in nine days the R. obtusi- 
folius became affected with iEcidium rumicus, the R. 
acetosa remains to this date (Oct. 31st) free. This method 
of experimenting in duplicate is a very valuable one, and I 
have frequently employed it inasmuch as it lessens the possi- 
bility of error. P. phragmitis was also applied to R. acetosa 
(177), but without result, as was also the case when P. Mag- 
nusiana was employed (139, 179, 206, 323). Of course, 
these are only negative results, but it is at least remarkable 
that I should have had no difficulty in producing iEc. rumicis 
on the other Rumices, but always have failed with R. acetosa. 
It happens, however, that upon Phragmitis Professor Oude- 
mans 3 has recorded the occurrence in Holland of P. straminis ; 
and in the early part of the year 1882 Mr. Bloome sent me, 
from near Worthing, a Puccinia on reed, which I regarded at 
1 Rostrup, * Heteroeciske Uredineer,’ p. 10 ; ‘ Observations nouvelles sur 
les Uredinees a generations alternantes,’ p. 3 ; ‘ Aftryk. af Oversigt over 
d. K. D. Yidensk. Selsk.,’ Fordhandl, 1884. 
2 Winter, ‘ Rabenhorst’s Kryptogamen Flora,’ 1881, p. 222. 
3 Oudemans, ‘ Bijdrage over niew ontdekte Champignons voor de Flora van 
Nederland,’ 1871, p. 22. 
