30 Proceedings 
3. Professor Neger, of Munich, states that conidia of the 
mildew on Ranunculus will infect Galium silvaticum. In 
this experiment the Ga/ium plant was protected by a bell- 
jar. Neger observes that the Ozdium they produced on the 
Galium had larger conidia than those of the Ozdium on 
Ranunculus. Again, the results of this experiment are 
unsatisfactory, because in Nature according to all exper- 
ience, the Mildew on species of Gadium is not the species 
which occurs on Ranunculus. 
Finally, Dr. Palla observed that in certain districts of 
Germany, Phyllactinia corylea attacks only bushes of bar- 
berry and hazel trees, notwithstanding that the trees, such 
as hornbeams, beech, birch, ash, &c., which in other dis- 
tricts are attacked by Phy//actinia, grew intermixed with 
the barberry and hazels. From this observation Palla con- 
siders that the morphologic species, Phy//actinia corylea, 
represents a collection of dzo/ogical species, each capable 
of growing only on certain host-plants. 
This is the whole of the existing evidence on the subject 
of the existence or not of biologic species in the Z7ys?- 
pacee. We see how inconclusive and fragmentary are the 
few experiments that have been performed. 
There is, I am convinced, a rich opportunity for the 
field-worker. There are numberless cases where out-of- 
door observations are required. For instance, every season 
in the autumn one notices that the leaves of the Vegetable 
Marrow become covered over with a mildew. This mildew 
is always found only in the conidial (Ozdium) condition. 
Now where does the mildew come from? The field-worker 
should take conidia from the mildews growing on any sur- 
rounding plants, and try to artificially infect the vegetable 
marrow. 
Indeed, so meagre is our knowledge on the subject of 
the dzo/ogical characters of the Erysiphace that the success- 
ful infection of any one host-plant by means of conidia 
taken from another would be a fact of really scientific im- 
portance. Of course it would be important to note all 
such details as atmospheric conditions, constitution of 
host-plant, time of year, attending the experiment. 
— 4 
