366 The American Naturalist. [April, 
Miscellaneous.—Perlitic structure, according to Mr. Chapman,™ 
may be produced in Canada balsam by heating this substance until it 
is thick enough to become brittle when cold, and then pouring it upon 
a roughened glass plate and suddenly immersing in cold water. 
Harker ascribes the eyes of pyrite in slate to the displacement of the 
matrix around pyrite crystals through pressure. Because of its hard- 
ness the pyrite resists the pressure. The slate yielding to it breaks 
away from the crystal along a plane perpendicular to the line of force, 
and leaves little hollows on both sides of it. The hollows are after- 
wards filled with quartz. The eyes consist of pyrite, forming a center, 
imbedded in a lenticular mass of quartz or some other secretionary 
mineral. In a book of about two hundred and seventy pages Mr. 
. Merrill* publishes a catalogue of the building stones in the collection 
of the National Museum, and gives a very clear and succinct account 
-of the methods employed in quarrying and finishing the various rocks 
used in construction, A very valuable account of the mineral re- 
sources of Michigan is given by Mr. Lawton % in his annual report as 
Commissioner of Mineral Statistics of Michigan. Dick * describes 
a new form of binocular microscope for use in petrographical investiga- 
tions, made according to his own design. The most important new 
feature of the instrument is the connection of the two nicols, which 
may be made to revolve together or separately, at the will of the man- 
ipulator. 




BOTANY. 
Three Suggestions on Botanical Terminology.—So far as I 
can find there are at least two very marked and interesting phenomena 
in the physiology of plants which have as yet received no appropriate 
names by which they may be always recognized and under which they 
may be disc . These are—first, the peculiar irritability of twining 
plants, in view of which, together with their negative geotropism and 
their asymmetrical nutations, the spiral habit of growth is maintained. 
From the most recent researches it appears probable that Von Mohl 
was correct in his early conjecture that some such specific irritability 
existed in twining plants, and it is proper that this specific irritability 
22 Geol. Mag., a 1890, p. 79. 
23 Ib., Sep., 1889, 
% Rep. ae Taaa tt Pt IL 
% Mines and Mineral Statisti Lansing, 1889. 
26 Min. Mag., March, 1889, a 160. 
