DUBLIN MICROSCOPICAL CLUB. 413 
abnormal forms of fructification. This may possibly have been 
the case in the instances quoted by Magnus in ‘ Die botanischen 
Ergebnisse der Nordseefahrt’ (1872), but it must always be a 
matter of great difficulty to decide as to the presence of such 
forms in dried specimens of alge, as are for the most part met 
with in collections. Magnus declares that the bodies figured by 
Harvey (‘ Phycologia Australis,’ Pl. CCXXVII), as probably 
Antheridia in Callithamnion dispar are only specimens of Chytri- 
dium plumula, Cohn. Dr. Wright now exhibited mounted 
specimens taken from the identical form figured by Harvey, 
which, though differing materially from the figure, where the 
globose bodies in the end cells are, owing to an oversight, printed 
red in place of yellow, still did not seem to show any marked 
character of Chytridium. The subject opened up a wide field, well 
worthy of being closely investigated on the living alga. 
Minute Structure of the Leaves of Pinus grandis, Douglas, 
and P. lasiocarpa, Hooker.—Dr. McNab exhibited sections of 
the leaves of Pinus grandis, Douglas, and of P. lasiocarpa, 
Hooker, and pointed out that, although the two names were 
generally considered to apply to the same plant, still, Pimws lasio- 
carpa, Hooker, was quite distinct from Pinus grandis, Dougl., and 
was apparently not in cultivation in this country. The two forms 
can at once be separated by the position of the resin canals in the 
leaf: P. lasiocarpa has the resin canals in the middle of the 
parenchyma, whilst in P. grandis they are close to the lower 
epidermis and near the margin of the leaf. 
Structure of Spine of Strongylocentrotus tuberculatus.—Mr. 
Mackintosh showed the spine-structure of Strongylocentrotus 
tuberculatus, which corresponds in type with that of Strongylo- 
centrotus armiger (see ‘Club Minutes’ of April, 1875), but 
differs from it m having the solid pieces more quadrilateral than 
triangular, and in the more open character of the network both 
in the central portion (“ pith,’’ C. Stewart) and in the radiating 
spokes. 
(Edogonium macrandrum,, Wittr., for the first time shown as 
Irish, and other species exhibited—Mr. Archer showed the above, 
also Cdogonium acrosporum, De By., as well as Cidog. 
Areschougu, Wittr.; all must seemingly be accounted as rare 
with us. 
Composition of Volcanic Dust from St. Vincent.—Professor 
Hull, F.R.S., exhibited under the microscope a little of the fine 
Volcanic Dust which fell on the Island of Barbadoes on May- 
day, 1812, having been discharged into the air from the great 
volcano of St. Vincent during the eruption which commenced 
three days previously, and at a distance from Barbadoes of 100 
miles. The dust was found to consist of angular or sub-angular 
grains of two kinds of felspar (sanidine and_ plagioclase), 
together with grains of magnetite, which were readily attracted 
by a small magnet. The grains of dust were so small as to be 
