BRITISH HETER(ECIOUS UREDINES. 89 
conclusion that the corresponding spore-forms probably occurred 
upon Phalaris arundinacea. There was only one cluster of this 
grass in the lane, and this was at the spot where the Zeidium Ari 
occurred. Moreover, the Phalaris was affected very extensively 
with a Puceinia. Upon microscopic examination these teleuto- 
spores corresponded so closely with those of P. sessilis, Schn., as to 
be practically undistinguishable from them in form and size—the 
only point of difference being that in my plant the teleutospores 
were surrounded by a bed of dark brown tissue, very much like 
that of P. rubigo-vera, but the individual hyphæ were not at all 
easy to separate. Although this character is not mentioned in con- 
nexion with P. sessilis, yet it might be due to some accidental 
condition of growth; so that I was, at first, rather doubtful as to 
the possibility of my plant being connected with the ZEcidium of 
the Arum; for P. sessilis has been proved to have its :ecidiospores 
upon Alliwm ursinum. On the other hand, I had previously met 
with a Puccinia on Phalaris, near King's Lynn, which I had 
always taken for P. sessilis ; and had, upon more than one occa- 
sion, tried to infect Allium ursinum with it, but always without 
success. In fact, the connexion between Zeidium Allii and 
P. sessilis had always been a puzzle to me, for the Æcidium does 
not occur in this locality, although the supposed P. sessilis does. 
On 25th April, 1885, a series of cultures were made with the 
Puccinia on Phalaris, from Gayton, upon seven plants of Arum 
maculatum. In the course of eleven days the spermogonia began 
to manifest themselves and, in due time, the ZEcidiwn. Con- 
versely, a number of cultures were made with the spores of Heidiwm 
Ari on Phalaris, which gave rise to the Uredo and Puccinia. The 
Uredo, furthermore, was found to differ from that of P. sessilis 
in having yellow instead of brown uredospores. A duplicated 
experiment was also made, in which a quantity of freely germi- 
nating Puccinia-spores was divided into two portions, one of 
which was placed on a plant of Arum maculatum and the other 
upon several plants of Allium ursinum. The Arum became af- 
fected with the ZEcidium, but all the Allium plants remained free. 
Hence it is evident that ZEcidium Ari is an heterecious uredine, 
having its corresponding uredo- and teleutospores upon Phalaris 
arundinacea ; and that it is specifically distinct from the plant 
described by Schneider as Puccinia sessilis, from which it differs 
in having yellow uredospores and in the teleutospores being 
surrounded by a dark brown bed of tissue. The two Puccinie 
