Feb., 1889. 
NEW BOOK ON LEAF-FUNGI. 
47 
confused together ; there are now known to be three :— 
Puccinia phragmitis ( = P. arundinacea), the secidia of which 
grow upon Rumex conglomeratus, obtusifolius, crispus, Hydro- 
lapathum , Rheum officinale; P. trailii, the secidium of which is 
confined to Rumex acetosa; and P. magnusiana, which has its 
secidia on Ranunculus repens and bulbosus. But this is not all. 
An secidium also occurs on R, bulbosus which is scarcely 
distinguishable, morphologically, from the one just mentioned, 
but which belongs to a Uromyces having its teleutospores 
on Dactylis glomerata, and another Uromyces, having its 
teleutospores on species of Poa, has its ascidia on R. bulbosus 
and repens , as well as on R. Ficaria. Still further to complicate 
matters, another Uromyces occurs upon R,. Ficaria , which 
has been proved to have no connection with the secidium upon 
the same plant. Once more, there is still another Uromyces 
which grows upon all the species of Rumex mentioned above 
(including R. acetosa ), but which has no connection at all with 
any of the other parasites. Finally, the secidium on 
Ranunculus acris , which used to be undistinguished from those 
on the other Ranunculi , is found to belong to a species ( Pucc . 
perplexans ), which it was reserved for Mr. Plowright to 
discover. 
It must be remembered that all these statements have 
been proved by experimental cultures, in which not only the 
positive results must be regarded, but also the negative results 
obtained in the various methods of “ control ” cultures. The 
latter, indeed, are far more convincing than the former. If, 
on sowing the spores of an tecidium on another plant, we 
obtain a Puccinia, the result may be put down to chance, and 
was explained in this way by the older school. But if, in a 
series of similar experiments, we find that the Puccinia 
invariably appears where we have sowed the secidium, and 
invariably does not appear (if proper precautions be taken) 
where the spores of the secidium have not been applied, the 
conclusion that the one is produced from the other becomes 
very probable. If again, on sowing the promvcelial spores 
obtained from the Puccinia on a suitable host, we invariably 
get the secidium with which we started, and don’t get it (under 
similar conditions) when the Puccinia has not been applied, 
the demonstration is complete. When these results are 
confirmed by hundreds of experiments made by observers of 
different nationalities, it is mere fatuity to doubt any longer. 
I have been led into this digression because undoubtedly 
the chief value of Mr. Plowright’s book lies in its biological 
aspect, but it is also an enormous advance upon all previous 
English works in its morphological descriptions, which may be 
