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TOTTEN - AL OE THE EOYAL HORTICULTURAL SOCIETY. 
would show all stages intermediate between wbat are regarded as 
the typical forms of Uncinula spiralis and U. americana. ’ Alto¬ 
gether there appears to he no greater difference between them 
than such as may reasonably be attributed to the variability of a 
single species. 
Uncinula subfusca, B. & C.—This is another North American 
species of Uncinula which occurs on the leaves of Ampelopsis 
quinquefolia, although we have no evidence of its having occurred 
on a true species of Vitis. The manuscript name of Uncinula 
ampelopsidis has also been applied to this species, but it was not 
published, in so far as we are aware, previous to the description by 
Berkeley and Curtis. Compared together under the microscope, 
there is a considerable difference between this and Uncinula 
spiralis. The fulcra are shorter, more robust, fewer in number? 
and rather more decidedly coloured. Perhaps the internal 
structure does not differ to any appreciable extent. If any two of 
these forms are to be regarded as distinct species, the third must also 
be recognised as such, since the points of divergence are the same 
in all. Por our own part we should prefer to regard them as 
three varieties of the same species ; but it is exceedingly difficult 
to induce botanists who confine their observations to their own 
flora, to admit the extent to which variability in a single species 
may be induced by a change in the external circumstances under 
which it may be produced.* 4 In this instance a different foster - 
plant may make all the difference in the length of the fulcra, 
which after all is the chief distinction. 
None of the three forms have as yet been discovered beyond 
the limits of North America. 
Note. — Splicerotheca mors-unce^ Schwz.—This is the one solitary 
instance of a species of Splicer otheca, having been found on Yines. 
It was first described by Schweinitz nearly fifty years since as 
occurring on Grapes in the United States, where it certainly seems 
to be rare, since it is seldom mentioned by American mycologists. 
Although described as a species of Erysiphe , the Eev. JI. J. 
Berkeley has referred it to the genus Splicer otheca, but we have 
never had the fortune to see a specimen, and therefore can add 
very little beyond the name, which even had passed from our 
memory when the above communication was made to the Scientific 
Committee. 
* Compare Uncinula adunca as developed on ’Willow with specimens 
grown on Poplar for a confirmation of this. 
