At the last meeting of the New York Microscopical Society, a paper
was read by Dr. Samuel Lockwood, secretary of the New Jersey State
Microscopical Society. His subject was the Wine Fly, _Drosophila
ampelophila_. The paper was a contribution to the life-history of this
minute insect. He had given in part three years to its study, beginning
in September, 1881, when nothing whatever of its life-history seemed to
have been known. In October the flies attacked his Concords. He found
upon a grape which he was inspecting with a pocket-lens an extremely
small white egg; but lost it. The grapes when brought on the table were
infested by the flies, which proved to be the above mentioned species.
When driven from the grapes they would fly to the window, where he
captured two of them These were placed in a jar with a grape for food.
In two days he found one egg on the outer skin of the grape. The laying
was kept up for four or five days, until there were about thirty, some
on the outside of the grape and some at an opening where the two flies
had fed. The egg had a pair of curious suspenders near the end where
the mouth of the larva would develop. These suspenders were attached at
their ends to the grape, but where the egg was laid in the soft part of
the fruit the suspenders were spread out at the surface; thus the larva
would emerge clean from the shell. The egg was 0.5 mm. in length, and
about a fourth of that in width. The larva when grown was at least four
times as long as the egg. As the larva burrowed in the juices of the
fruit, two quite prominent breathing tubes at the posterior end were
kept in the air. Between these cardinal tubes were several teat-like
points, much smaller, but having a similar function.
The larvae appeared in five days after the eggs were laid. In about as
many more days the puparium state would be entered, and in about six
days more the fly or imago would appear. In ovipositing the suspensors
would leave the oviparous duct last. The paper claimed that the curious
shape of the egg compelled the female to oviposit slowly, as it took
time for the egg to assume its form; hence, the eggs were not laid in
strings or masses, but singly and at considerable intervals.
The flies are very hairy, especially the females. The neck and even the
eyes are very hirsute. The eyes are red, quite large and pretty, though
somewhat _outre_ under the microscope, for from between the little
lenses are projecting, straight, stiff hairs. As the insect is quite
active, it must be that this fringing of the tiny eyelets with hair does
not materially obscure its vision. When the minuteness of this singular
arrangement is considered, it is surely remarkable. This general
hairiness of the female especially, and that about the head, neck, and
forward part of the thorax, stands correlated to a beautiful structure
found only in the male, which has on the tarsus of each leg in the
forward pair what the lecturer called a sexual comb. It is a beautiful
comb of a very dark brown color, each comb having ten pointed and strong
teeth. In the nuptial embrace these combs are fixed in the hairy front
of the thorax of the female, thus becoming little grapnels.
The flies love any vegetable substance in fermentation, whether acetic
or vinous. Hence it will abound about cider mills, swarm on preserves in
the pantry, and in cellars or places where wine is being made or stored.
The paper showed the tendency of the glucose in the over-ripe grape
to the vinous ferment, and that the fly delighted in it. A singular
accident showed how they loved even the very high spirits. In making
some of the mounts shown to the society, Dr. Lockwood had left a bottle
of 90 per cent. alcohol uncorked over night. Next morning he was
astonished to find his alcohol of a beautiful amethystine color, and the
cork out. Inspection showed a number of these tiny creatures, which,
when filled with the purple juice of the grape, had smelt the alcohol
in the open bottle, and had gone in to drink. They had ignominiously
perished, and had given color to the liquid.--_Micro. Journal_.
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[NATURE.]
THE "POTETOMETER," AN INSTRUMENT FOR MEASURING THE TRANSPIRATION OF
WATER BY PLANTS.
In view of the interest now attaching to recent advances in vegetable
physiology, it seems not unlikely that a description of the instrument
bearing the above name, lately published by Moll (_Archives
Neerlandaises_, t. xviii.), will serve as useful purpose. The apparatus
was designed to do away with certain sources of error in Sachs'
older form of the instrument, described in his "Experimental
Physiologie"--errors chiefly due to the continual alteration of pressure
during the progress of the experiment.
As shown in the diagram, the "potetometer" consists essentially of a
glass tube, a d, open at both ends, and blown out into a bulb near the
lower end; an aperture also exists on either side of the bulb at or
about its equator. The two ends of the main tube are governed by the
stopcocks, a and d, and the greater length of the tube is graduated. A
perforated caoutchouc stopper is fitted into one aparture of the bulb,
e, and the tube, g k, fits hermetically to the other. This latter tube
is dilated into a cup at h to receive the caoutchouc stopper, into which
the end of the shoot to be experimented upon is properly fixed.
The fixing of the shoot is effected by caoutchouc and wire or silk, as
shown at i, and must be performed so that the clean-cut end of the
shoot is exactly at the level of a tube passing through the perforated
stopper, e, of the bulb; this is easily managed, and is provided for by
the bending of the tube, g h. The tube, f, passing horizontally through
the caoutchouc stopper, e, is intended to admit bubbles of air, and so
equalize the pressure and at the same time afford a means of measuring
the rapidity of the absorption of water by the transpiring shoot. This
tube (see Fig. 2, f) is a short piece of capillary glass tubing, to
which is fixed a thin sheath of copper, b', which slides on it, and
supports a small plate of polished copper, a', in such a manner that the
latter can be held vertically at a small distance from the inner opening
of the tube, and so regulate the size of the bubble of air to be
directed upward into the graduated tube, a b.
[Illustration]
The apparatus is filled by placing the lower end of the main tube under
water, closing the tubes, f and i (with caoutchouc tubing and clips),
and opening the stopcocks, a and d. Water is then sucked in from a, and
the whole apparatus carefully filled. The cocks are then turned, and the
cut end of the shoot fixed into i, as stated; care must be taken that no
air remains under the cut end at i, and the end of the shoot must be at
the level, k l. This done, the tube, f, may then be opened.
The leaves of the shoot transpire water, which is replaced through the
stem at the cut end in i from the water in the apparatus. A bubble of
air passes through the tube, f, and at once ascends into the graduated
tube, a c. The descent of the water-level in this tube--which may
conveniently be graduated to measure cubic millimeters--enables the
experimenter at once to read off the amount of water employed in a given
time.
It is not necessary to dwell on obvious modifications of these
essentials, nor to speak of the slight difficulties of manipulation
(especially with the tube, f). Of course the apparatus might be mounted
in several ways; and excellent results for demonstration in class could
be obtained by arranging the whole on one of the pans of a sensitive
balance. H. MARSHALL WARD.
Botanical Laboratory, Owens College.
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