NOVEMBER,
Volume XVI. 1915 Number 1.
The Ohio
Journal of Science
(Continuation of The Ohio Naturalist)
Official Organ of the
OHIO STATE UNIVERSITY SCIENTIFIC SOCIETY
and of the
OHIO ACADEMY OF SCIENCE
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THE OHIO JOURNAL OF SCIENCE
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CLAYTON MCPEEK Physiology (Medical)
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J. S. HINE Zoology and Entomology
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THE OHIO JOURNAL OF SCIENCE
PUBLISHED BY THE OHIO STATE UNIVERSITY SCIENTIFIC SOCIETY
VOLUME XVI NOVEMBER, 1915 NO. 1
TABLE OF CONTENTS
INTRODUCTORY 1
LORD—The Making of a Photographic Objective 3
TRANSEAU—Notes on the Zygnemales 17
Organization of the Ohio State University Scientific Society 32
INTRODUCTORY.
Fifteen years ago the Biological Club of the Ohio State University
began publishing THE OHIO NATURALIST. This Journal has had a continuous
existence and has been an important medium in advancing the knowledge
of the natural history of the state. A number of years ago the
NATURALIST became the official organ of the Ohio Academy of Science
and was thus sent to every member of the Academy. At that time the
Ohio Academy was largely composed of Biologists and Geologists, but
has now widened its scope to include Physicists, Mathematicians, and
others. It was, therefore, thought desirable by many that the scope of
the NATURALIST should be enlarged so as to make it representative of
all of the activities of the Academy. In accordance with this desire,
committees were appointed by the various departments interested and a
plan for future publication was proposed which was finally adopted.
The Ohio State University Scientific Society was thus organized at
the Ohio State University and will take over the control of the new
publication. This Society is to have somewhat the same relationship
to THE OHIO JOURNAL OF SCIENCE as the Biological Club had to the Ohio
Naturalist. The management of the Journal is under an Editorial Board
made up of representatives of various scientific departments of the
University. This Board elects annually the Editor and two Associate
Editors.
EDITORIAL BOARD.
Agricultural Chemistry, J. F. Lyman; Agricultural Engineering, F. W.
Ives; Agronomy, A. G. McCall; Anatomy, F. L. Landacre; Botany, J.
H. Schaffner; Ceramic Engineering, Carl B. Harrop; Chemistry, Jas.
R. Withrow; Civil Engineering, F. H. Eno; Forestry, N. W. Scherer;
Geology, C. S. Prosser; Horticulture, V. H. Davis; Industrial Arts,
W. A. Knight; Mathematics, C. J. West; Mechanical Engineering, Horace
Judd; Pathology, Jonathan Forman; Physics, F. C. Blake; Physiology
(General) R. J. Seymour; Physiology (Medical), Clayton McPeek; Public
Health and Sanitation, E. R. Hayhurst; Zoology and Entomology, J. S.
Hine.
THE OHIO JOURNAL OF SCIENCE is to be considered as a continuation of
THE OHIO NATURALIST. It is hoped that with the wider field covered,
it may interest a much larger number of the scientific people of the
state, and be financially supported so that it may soon develop into a
journal of high standard. It is the intention of the present Editors,
with the large field before them, to publish results of research as
well as articles of general interest in the advancement of Science.
On the natural history side the aim at present will be to pay more
especial attention to the biology, geology and geography of Ohio, but
articles dealing with any other region will be acceptable.
The Editors for the present year are as follows:
John H. Schaffner—Editor.
James S. Hine—Associate Editor (Business).
Frederick W. Ives—Associate Editor (Subscriptions).
JOHN H. SCHAFFNER.
THE MAKING OF A PHOTOGRAPHIC OBJECTIVE.
Being a Description of a Course in Applied Optics Offered at
the Emerson McMillin Observatory of the Ohio State University.
H. C. LORD.
Photography, in its more serious phase, has taken an important place
in almost every field of human activity while in its lighter mood,
through the development of the “Kodak” and the roll film, is giving us
one of our most delightful pastimes. As a condition for the best work,
a high grade lens is a necessity and especially so for those extremely
short exposures required in the photography of rapidly moving objects.
It often happens that some of the most perfect and at the same time
most difficult specimens of optical design are found on cameras so
small that they can be easily carried in one’s coat pocket. These so
called anastigmats furnish to the optician a difficult and yet at the
same time most fascinating problem for mathematical investigation.
Thousands of photographic objectives are placed on the market every
year, yet though almost every branch of engineering is covered by
our technical schools, I know of no place outside of Germany where a
student can be instructed in the design and construction of a simple
photographic objective. Professor Silvanus P. Thompson in his inaugural
address as President of the British Optical Convention held in London
in 1912, states: “In the Universities and Colleges the only people who
are learning Optics are merely taking it as a part of Physics for the
sake of passing an examination for a degree, and care nothing for the
application of Optics in the industries. They are being taught Optics
by men who are not opticians, who never ground a lens or calculated
even an achromatic doublet, who never worked an opthalmoscope or
measured a cylindrical lens.” Further on he speaks as follows: “What
is wanted is an establishment where the whole atmosphere is one of
optical interest; where theory and practice go hand in hand; where the
mathematician will himself grind lenses and measure their performance
on the test bench; where braincraft will be married to handcraft;
where precision, whether in computation or workmanship, will be the
dominating ambition.”
Some four years before the above quotations were written, the author
started to work up a course in Optics which should aim, not only to
give to the student a knowledge of the fundamental theory of lenses,
but should also apply those principles to the methods of optical design
and thus enable him to compute the curves of the component lenses of a
photographic objective. This has now been fairly well worked out and is
given in the Arts college under the official titles “Astronomy, 107,
108, 109 and 110.” The basis of this course is “A System of Applied
Optics,” by H. Dennis Taylor, the inventor of the Cooke lens. This
splendid volume develops, from the standpoint of geometric optics, a
complete discussion of the formation of an image by a combination of
any number of lenses, but does not apply the methods and formulae there
developed to the actual design of a photographic objective. The writer
of this paper was, therefore, compelled to work out this part of the
theory for himself and, as he had always felt that all mathematics
should ultimately end in arithmetic and that all arithmetic should
ultimately end in doing something, he resolved at the outset that
the course should end in laboratory work in the actual computation,
grinding and polishing of lenses. As to how well this has succeeded,
I will let the illustrations which accompany this article speak for
themselves. Suffice it to say that the half tone cuts were made from
five by seven enlargements from negatives, one and three quarters by
two and one-eighth inches, taken with a lens _designed_ and _built_
at this observatory and working at an aperture of F six. A peculiar
feature of this lens is that it is composed of four lenses all cut
from the same piece of crown glass. This lens beautifully illustrates
the importance of adding to the theoretical side of the course, the
practical work in the laboratory in construction and testing as this
lens, though in the main satisfactory, has one serious defect and a
defect which is very instructive in that it shows that at a certain
point in the design, the theory was weak and needed to be extended and
enlarged. It should be stated that this theoretical investigation is
now completed and ready to be put to the test of practice.
This Observatory possesses a well equipped instrument shop, which was
used for the practical side of this work and it has seemed to me that
a description of how we used the ordinary tools of a machine shop, of
what special appliances we were compelled to make, and how we finally
ground and polished our lenses would be of general interest. These
methods do not pretend to be the best, nor those actually employed by
the manufacturer, but they do illustrate how a lens can be made and how
a little ingenuity will enable one if he has the standard tools of a
machine shop to carry out almost any kind of experimental work.
As a preliminary to this, a brief outline of the problem before the
lens designer may be of interest. A simple lens consists of a piece of
glass bounded by either plane or spherical surfaces as these, except
in large reflecting surfaces, are the only kind that can be made with
sufficient accuracy. Such a lens would have a great many defects or
errors and would be unable to give a sharp image on the photographic
plate unless stopped down to a very small aperture. By changing the
radii of the surfaces, and the thickness of the lens, the designer can
vary these errors, but after all is said and done he can do but little
to improve the single lens. He then combines lenses of different forms
and of different kinds of glass into a single objective, in this way
making the positive errors of some of the lenses balance the negative
errors of the others, until he arrives at a combination which is more
or less perfect according to his skill as a designer. How this is
accomplished is far beyond the limits of this paper, so I will now
proceed to the mechanical side of the problem.
The first consideration is the glass; of course it must be what is
known as optical glass and its selection is really part of the work of
the designer. Optical glass is nothing more than a very perfect kind
of glass which has been exquisitely annealed. You are all familiar
with the intense green of window glass when seen edgewise; a piece of
white paper will hardly be changed in color when seen through twelve
inches of a good optical crown. The best optical glass is not made in
this country, but must be purchased from either Schott & Gen. of Jena
or Mantois of France. The Jena glass has become very celebrated and
most of the lens makers state that their lenses are made out of it and
as a consequence most people think that Jena glass means a certain
kind, while, as a matter of fact, their catalogue for 1909 shows about
seventy different varieties. These differ in optical qualities and
chemical composition, and cost from about a dollar to five dollars a
pound, with a few special varieties costing as much as fifteen dollars.
This glass comes in slabs, but will be cut by the makers with either a
diamond saw or a sand saw, the purchaser paying for the “saw dust.”
[Illustration: FIG. 1]
[Illustration: FIG. 2]
The slabs that were used here were 2" × 6" × ½" and the first operation
was to cut from these round disks a little larger than the finished
lens. This was accomplished in the following manner and is illustrated
in Fig. 1. In the chuck of a drill speeder on a Barnes drill press was
placed a ¼" steel rod which carried at its lower end a copper tube,
A, which was steadied at the bottom by a steel washer, bored to a
loose fit to the tube, and clamped to the glass as shown. Number 40
Carborundum was used and lubricated with _plenty of water_. The tube
must be lifted frequently to allow the abrasive to flow to the cutting
edge. This is done so often that it seems almost a continuous motion of
lifting and pressing down again, the tool resting on the glass hardly
more than two or three seconds at a time. The cutting may be done at
such a speed as to allow of a slight heating. As soon as the tube has
cut itself about a sixteenth of an inch into the glass, the guiding
washer may be removed and the glass will then act as its own guide. A
disk about one inch in diameter and a half of an inch thick could be
cut out in a little over a half of an hour. At B Fig. 1 is shown one
of the uncut slabs and at C and D two that are about used up. Though
working rather slowly this proved quite satisfactory though wasteful
of glass as it cut a rather wide scarf, copper must be used; brass was
tried but the wear was so great as to render it almost useless while
the copper shows almost none.
As these disks are cut out they are not only cone shaped but the edges
are very rough so that the next operation was to grind these to smooth
and true circular disks. This was done on a Wells tool grinder shown
in Fig. 2, which was slowed way down by placing a large pulley on the
counter shaft. The glass to be ground was held by cementing it with
pitch onto a piece of brass rod which in turn was held in the drawing
collet of the head A. A special wheel B, made by the Norton people
for grinding the rims of spectacle lenses, was used and the machine
slowed until the wheel would keep wet when running against a sponge,
C, resting in water. The glass disk was in this way kept dripping and
heating entirely prevented. The grinding was then carried out just as
with any other material and the edge was made beautifully smooth and
true in a few minutes. The beauty of pitch as a cement for holding the
glass is that a slight heating will soften it so that the disk can be
shifted to any position and then a dash of cold water clamps it in
place and at the same time the pitch will slowly yield to the slightest
pressure so that in a few minutes the glass is entirely free from
strain. In manufacturing this sort of work is done with a diamond and
is of course done much more quickly.
The disks were thick enough to make two lenses each so we sawed them
into two as illustrated in Fig. 3. A is an old polishing head upon
which was mounted a pulley at one end and a copper disk, B, at the
other, the disk being held between large washers. C is a cast iron box
fastened to an arm, D, hinged at E and kept pressed against the copper
disk by a cord passing over two pulleys on the ceiling. This made a
most excellent automatic feed. The glass to be split was fastened to
a block of pine with pitch and the wood held in the iron box, C, with
wedges. Number 40 Carborundum was used with plenty of water and the
glass was cut through faster than a power hack saw would cut through
steel. The glass should be cut half way through and then reversed so
that the final break will come in the middle and thus prevent the edges
from spawling off. The chief defect of this machine was the way it
scattered emery.
[Illustration: FIG. 3]
The disks are now ready for the grinding which is done on the machine
on the right of Fig. 3, which consists simply of a vertical spindle
run by a quarter twist belt from the counter shaft against the wall.
The end of this spindle is tapered at the upper end to receive the
grinding tool or laps, shown on the table in Fig. 5 which also shows
the spindle raised so that the grinding lap is seen above the tin box,
C, which surrounds the spindle to catch the abrasive that is thrown off
in grinding. The glass is first smoothed down on a flat lap until it is
of equal thickness at all points as measured by a micrometer when it is
ready to be ground to the proper curves. For this purpose the spherical
laps, shown in Fig. 5, are turned in the special machine illustrated in
Fig. 4. The compound rest of an old Seller’s lathe was removed and in
its place, on the cross slide of the carriage, was mounted the sphere
turning rest. This consists of a base, A, in which the slide, B, is
so mounted that it can be rotated about the center, C, by turning the
milled head, D, which carries a worm at the opposite end. E is the
tool post with the cutting tool T and L the lap to be turned. A hole
was drilled at C into which was fitted a round piece of steel the
upper end being pointed and then half cut away like a center reamer.
This was used in finding the zero; the rod, pointed end up, was placed
in the hole at C and the cutting tool adjusted against the flattened
side. The zero position is then determined by measuring, with an inside
micrometer, the distance from the tool post to a stop placed at the
end of the slide B. By adding to or subtracting from the zero reading
of the micrometer the length of the radius of the grinding lap, the
tool post may be set to the proper position for either a convex or a
concave surface. This, however, is only approximate, for these laps
must be made with the highest possible accuracy. After sufficient cuts
have been taken to give a spherical surface, the radius is carefully
measured with a special spherometer and the error in the radius
corrected by changing the position of the cutting tool by an amount
calculated from the readings of the spherometer. This spherometer we
were compelled to build as we could find none of sufficient accuracy on
the market and it is described in a note at the end of this article.
[Illustration: FIG. 4]
[Illustration: FIG. 5]
In Fig. 4, R is simply a steady rest made with the large overhang
to allow the slide B to swing under it in turning a convex surface.
Two master laps, male and female, must be made and carefully ground
together. Every effort should be taken to make these as accurate as
possible since upon these depends the goodness of our lens. This
special tool is easy to make and leaves nothing to be desired in its
operation. Detail drawings and directions for making it are given in a
note at the end.
We now come to the grinding or lapping of the lenses themselves. This
is done in a lap turned as above and carefully fitted to the master
laps and which must be trued from time to time as the work progresses.
This lapping of glass is entirely different from the lapping of metals
in that, while in metals the lap is to be kept almost free from the
abrasive, in glass the lap must be freely supplied with emery and water
or deep scratches will result. The best way to apply the emery is with
a paint brush; the brush, saturated with emery, being held in front of
the lens as it is ground. The lens may be held in the hand or cemented
to a disk of brass having a center hole drilled in the back in which is
placed a pointed piece of steel held in the hand, the lens being free
to rotate about the pointed steel holder. Of course where the lens has
to be ground to a definite thickness it must be held by hand. Flour of
emery was used to rough grind though coarser grades would have worked
faster. The final smooth grinding was done with a special fine emery
made for this purpose by Bausch and Lomb. Great care must be taken in
the grinding to keep the lens as nearly centered as possible. A lens is
said to be centered when the line which joins the centers of curvature
of the surfaces passes through the center of figure. Obviously if a
double convex lens could be ground to a knife edge it would be centered
but if this were done the edge would be almost certain to crumble
in the final polishing and deep scratches result. The centering of
a convex lens can be watched by keeping the edge as nearly uniform
of thickness as possible with a concave lens, if the original blank
is made larger than necessary and care is taken to make the sides
parallel, the centering can be watched by keeping a flat edge of _equal
width_ around the concave portion, the lens being placed back on the
flat tool, from time to time, as the work progresses. If care is used
the lens need be made but little larger than the finished size to allow
for the final accurate centering to be described later.
After being smooth ground the lens is beautifully smooth and velvety
to the touch but is just as much ground glass as ever, that is, it is
absolutely opaque. We now come to the polishing. This is done with
specially prepared rouge and only an excessively small amount of glass
is taken off. Lord Rayleigh in a paper on “Polishing of Glass Surfaces”
read before the British Optical Convention held in 1905, states: “I
started with a finely ground surface, rather more finely ground I think
than is used in practice, and I found that in order to obtain a pretty
good polish it was necessary to remove a weight of glass, corresponding
to a depth of about 6 wavelengths. I do not pretend that such a polish
would satisfy the requirements of commerce; probably the 6 would have
to be raised to 10 or 12 in order to get to the bottom of the deepest
pits.” When it is remembered that a wave length is about the fifty
thousandth part of an inch we realize how very delicate such lapping
must be. For this work the lap is covered with pitch which has been
brought to the proper degree of hardness either by boiling, to harden
it or by adding asfalt varnish to soften it. The proper degree of
hardness is very important and must be adjusted to the temperature of
the room. Obviously if the pitch is too soft it will not hold its shape
and it will be impossible to hold the polishing tool to the proper
radius. I have put three different curves on a lens about an inch in
diameter in a few minutes and it had to go back on the grinding machine
before it could be finished.
The polishing tool is prepared as follows: A disk of pitch, about ¼"
thick, is cast by pouring it in a mold made by a strip of brass bent
to a circle, the ends clamped with a tool maker’s clamp, and rested on
a piece of cold cast iron which has been planed smooth. This should be
of such size that when bent to the proper shape it can be molded over
a tool similar to the grinding tool but with a radius changed by about
the thickness of the pitch. This tool is then heated and painted with
a stick of pitch, the disk is warmed, and the two pressed together,
when cooled the pitch will stick tight to the iron but will be far from
a smooth surface. This and the master tool of the opposite curvature
are placed in warm water and pressed together and at the same time one
slowly rotated, one about the other. When a good fit is secured they
are cooled and a number of small holes, about 1-8" in diameter, are
drilled all over the pitch to distribute the abrasive, which of course
spoils the surface and the tool must be again pressed. This pressing
to shape must be done repeatedly and requires great care and some
practice in order to have the pitch come to the exact opposite of the
pressing tool. The most important thing is to do the pressing slowly
and in fact in the whole process of this work one must never get in a
hurry. Ritchey, in his memoir on the construction of the great 60" at
Mt. Wilson, recommends covering the pitch with beeswax, and for quicker
and poorer work a cloth polisher may be used, the cloth being a special
felt and cemented to the cast iron tool with a thin layer of pitch.
The abrasive is rouge or red oxide of iron and its preparation is
fully described in the above mentioned work by Ritchey. We purchased
the anhydrous red oxide of iron from Merck & Co. This was mixed with
plenty of water in the jars shown at E, Fig. 5. The rouge will rapidly
precipitate, the coarse particles falling to the bottom, and leaving
clear water above the precipitated rouge. The upper two-thirds of the
rouge will be almost perfect and will give a beautiful polish when
carefully siphoned off. This should be kept in tightly corked bottles,
one of the best things is a horse radish jar as this has a place for
the handle of the brush in the glass stopper, and all dust and grit
can be easily washed off before the jar is opened. For polishing, the
lens is cemented to a handle at whose end is a piece of brass turned to
fit the lens in the sphere turning machine already described. Even in
a small lens the polishing tool must be run slowly, the speeds of our
machines run from 170 to 300 revolutions per minute and the fastest can
seldom be used. The reason of this is that the lens fits the polisher
so perfectly that almost a perfect vacuum is formed and the lens hugs
the polished so closely that it is impossible to hold it in small sizes
by hand alone and in the case of a convex surface, if the cavity is
carried clear out to the edge of the glass disk, this may be broken
simply by the friction due to this grip of the glass and pitch. Fig. 5
shows a horizontal polishing head at B and a vertical one at C. There
is little choice except that for convex surfaces B seems the best, as
it can be run faster, while for concave C seems better.
The lenses are now ready to be centered, that is, the circumference so
turned that the line which joins the centers of curvature of the two
spherical surfaces shall pass through the center of figure. In order
to accomplish this, the lens is first cleaned from the pitch used to
cement it to the handle used in holding the lens for polishing. For a
long time I could find no way of doing this satisfactorily when pitch
was the cement; finally, I laid my troubles before Dr. A. M. Bleile,
Head of the Department of Physiology, and he suggested to first soak
the lens in lard and then wash it in benzol (C_{6}H_{6}). This worked
like magic though the first time I tried it I used some lard that had
been heated with some pitch in it which made the lard very soft in fact
almost as soft as it could be and yet not be an oil, and this same lard
was used over and over again. The action is rather peculiar; the lard
does not apparently effect the pitch at all but after a few minutes in
the benzene it all flakes off and leaves the lens perfectly clean. The
actual centering is then carried out on the grinding machine shown in
Fig. 2; A holder, D, whose front face has been turned in the spherical
turning machine to fit one of the surfaces of the lens, is held in the
head A. If the lens be cemented to this with a thin coat of pitch,
it is obvious that the surface of the lens next to the holder will
have its center of curvature coincide with the axis of rotation of
the spindle of the head, A, but the center of curvature of the other
lens surface will probably fall outside of this axis. A lamp, L, has
a tin chimney with a pin hole in it turned towards the lens, this
pin hole forming a brilliant point of light, an image of which is
formed by each surface and reflected by the total reflecting prism,
P, into the telescope, T, where it is seen through the eyepiece. If
the centers of curvature of both surfaces do not accurately coincide
with the axis of rotation of the head, A, the images of the pin hole
will describe circles as this axis is rotated. The back surface will
of course be centered if the layer of the pitch used as cement is of
uniform thickness which will generally be the case if the work has
been carefully done; but in any case the image formed by it should
be examined. If the front surface is out of center, as it generally
will be, the holder should be warmed and the lens shifted, care being
used to keep it tight against the surface of the holder as it is being
shifted. As soon as both images remain stationary as the head, A, is
rotated, the lens is fed against the wheel, B, and ground true and to
size. This worked beautifully and the tests were wonderfully sensitive.
As soon as the component lenses of the objective have all been thus
centered, they are ready to be assembled in the cell or shutter in
which they are to be used; but as this is simply a matter of careful
machine work, I need not describe it further.
I know of no literature on the grinding of small lenses though the
following memoirs on the making of large reflecting telescopes should
be in the hands of any one interested in this work:
=On the Construction of a Five-foot Equatorial Reflecting Telescope.=
By A. A. Common, LL. D., F. R. S.
Memoirs of the Royal Astronomical Society, Vol. L., 1890-91.
=On the Construction of a Silvered Glass Telescope,
Fifteen and a Half Inches in Aperture, and its
Use in Celestial Photography.=
By Henry Draper, M. D.,
Smithsonian Contributions to Knowledge, Vol. 34.
=On the Modern Reflecting Telescope and the
Making and Testing of Optical Mirrors.=
By George W. Ritchey.
Smithsonian Contributions to Knowledge, Vol. 34.
NOTE 1—A SPHEROMETER FOR SHORT RADII.
[Illustration: FIG. 6]
In Fig. 6, A is a regular Brown & Sharpe Micrometer Head with the
measuring point ground to an angle of 60° and slightly rounded; B is a
round steel base all machined at one setting in which the micrometer
head is clamped by a set screw not shown.
Let r be the radius of the spherical surface, MNO, and we will have at
once r = (a^2 + d^2) / 2d. The advantage of this form of spherometer
is that it is very easy to make the point of the micrometer exactly
central with the base and the value of 2a can be accurately determined
by means of an ordinary micrometer calliper. For a convex surface,
2a should obviously be the inside diameter of the base, B.
In using the instrument, two tables, one for concave and one for
convex surfaces, should be prepared; these tables to give the power in
dioptres for each one thousandth of an inch in the value of d. Using
the American Optical Co.’s Standard Index, namely, μ equal to 1.5000
and one dioptre as being the power of a lens of 40 inches focus, we
have, for a plano lens, p = 4/f = 40d/(a^2 + d^2) since f = r/(μ-1).
The advantage of forming the table in dioptres in place of radii
directly is that the tabular differences are small at all parts of the
table so that interpolation can be readily done and this is not the
case in tables which give the radii directly.
If upon measuring the radius of the tool or lap being turned in the
sphere turning machine, Fig. 4, with this spherometer, the tool is
found to be in error by an amount Δp this may be corrected by changing
the position of the cutting tool by an amount 20 (Δp / p^2).
NOTE 2—CROSS SECTION OF THE SPHERE TURNING REST.
[Illustration: FIG. 7]
In Fig. 7 is shown a cross section of the sphere turning rest further
illustrated in Fig. 4. In machining this the following suggestions
should be followed. The piece M should be cast with a lug projecting
from the face PQ to chuck it by and all the turning done at one
chucking. It should be made a close fit to R and bolted tight against
DG and ED´ with the bolts S_{3} and S_{4}, clearance being given along
the line HF. To compensate for ware the face DG and ED´ can be releaved
from time to time with a file. The base N, should be planed along AB,
where it fastens to the cross slide of the carriage, then bolted to
a face plate of the lathe and finished, care being used to leave the
setting of the compound rest unchanged between machining the faces CD
and C´D´ of the pieces M and N. The dove tail on R should be first
planed and then this bolted to a face plate and the boss GHFE and the
faces KG and EL turned at one setting. If these directions are followed
almost no hand work will be needed. W is a brass worm wheel held by
screws not shown and J is the sliding tool post clamped at X with the
tool at K´.
NOTES ON THE ZYGNEMALES.[A]
EDGAR NELSON TRANSEAU.
The following notes principally concerning North American Zygnemales
are based on a study of the specimens accumulated in the course
of eight years collecting in central Illinois; a collection made
by Mr. Charles Bullard, of Cambridge, Mass., in Massachusetts
and New Hampshire; the specimens distributed in the Phycotheca
Boreali-Americana by Collins, Holden and Setchell; the specimens
distributed in American Algae, by Miss Josephine E. Tilden; the
specimens in the U. S. National Herbarium; and small collections sent
me by Professor Farlow, Miss Tilden, Professor A. B. Klugh, Professor
D. S. Johnson and Miss Grace Stone. They have been compared with the
species distributed by Wittrock and Nordstedt in their “Algae Aquae
dulcis exsiccatae,” and other valuable European and South American
specimens sent me by Professors O. Borge and O. Nordstedt.
In determining almost any species of the Zygnemales it is absolutely
essential that the specimens show both the vegetative cells and the
mature spores. With the exception of a few species of Mougeotia the
spores are colored either yellow, brown, or blue when they are mature.
The characteristic markings of the median spore wall do not develop
usually until this color appears. Consequently it is useless to attach
names to vegetative specimens based on dimensions and number of
chromatophores. Keys based on such characters are not only useless, but
misleading.
Judging from my experience in Illinois it is highly probable that the
list of North American forms will be considerably augmented, when
intensive studies have been made at localities in the Southern United
States. The most satisfactory method of collecting these forms is to
take samples from the various ponds and streams at regular intervals
of ten days, or two weeks, throughout the growing season. Many of the
species show local variations and considerable experience is needed
before many of the forms can be satisfactorily classified. The writer
has in course of preparation an illustrated key to the group, in which
figures for all of the species will be published.
=DEBARYA= Wittrock.
This genus is in many respects the most generalized of all the
_Zygnemales_. It is distinguished by three important characteristics:
(1) the entire contents of the gametangia enter into the making of the
zygospore; (2) the zygospore is formed in the conjugating tube and
is not cut off from the other parts of the gametangia by partition
walls; (3) as the gametes move toward the tube during conjugation,
their place is taken by a secretion of cellulose, which renders the
gametangia solid and highly refractive. This secretion also occurs when
a vegetative cell forms an aplanospore.
=Debarya glyptosperma= Wittrock.
This species has been recorded for America. It is not uncommon in
Massachusetts and has also been found in Minnesota and Florida. In
P. B.-A. No. 808 from Boswell, California is a somewhat smaller
variety with blue spores associated with _Zygnema peliosporum_ Wittr.
The spores are common in the material and the vegetative cells and
filaments occasional. Following is a diagnosis for this variety:
Var. =formosa= nov. var. Cellulis vegetativis 7.5-9µ latis;
zygosporis 24-30µ × 30-42µ, caeruleis; ceterum ut in typo.
Vegetative cells 7.5-9µ in diameter, zygospores 24-30µ × 30-42µ steel
blue, otherwise like the type.
=Debarya americana= nov. sp.
Cellulis vegetativis 9-12µ × 27-120µ, ad dissepimenta constrictis;
chromatophoris cum pyrenoidibus 2; cellulis fructiferis,
10-14µ × 75-180µ; zygosporis ovoideis vel quadrato-ovoideis,
20-40µ × 30-40µ, angulis rotundatis, productis, vel retusis;
parthenosporis 15-20µ × 20-30µ, oblique ellipticis, cum polis retusis;
mesosporio subtiliter et irregulariter verrucoso, maturitate
luteo-brunneo.
Vegetative cells 9-12µ × 27-120µ constricted at the end walls,
chromatophore with two pyrenoids; fertile cells 10-14µ × 75-180µ;
zygospores ovoid or quadrately ovoid, 20-40µ × 30-40µ, with angles
rounded, produced, or retuse; parthenospores 15-20µ-× 20-30µ
unilaterally ellipsoid with retuse ends; median spore wall minutely and
irregularly verrucose, yellow-brown at maturity.
This species was collected by Professor A. B. Klugh, Kingston, Ontario.
It is the material upon which the Ontario record for _Mougeotia
calcarea_ (Cleve) Wittr. is based. Of special interest is the
chromatophore with two pyrenoids, which although an axile plate is
distinctly two-lobed and forms an easy transition to the next species,
in which the chromatophore resembles _Zygnema_. Type in herb. E. N. T.
Collection No. 2950.
=Debarya decussata= nov. sp.
Cellulis vegetativis 16-20µ × 25-50µ cylindraceis; chromatophoris
asteroidiis duobus, singulis cum pyrenoidibus (ut in Zygnemate);
zygosporis vel ovoideis, vel irregularibus, 24-30µ × 30-48µ cum angulis
vel rotundatis, vel retusis, vel productis; aplanosporis uno latere
ovoideis, 17-25µ × 20-40µ; parthenosporis 15-20µ × 20-30µ; membrana
media sporarum scrobiculata, luteo-brunnea; akinetis ad dissepimenta
constrictis, membrana subcrassa et glabra, 18-20µ × 20-36µ.
Vegetative cells 16-20µ × 25-50µ cylindrical; chromatophores two,
stellate, each with a pyrenoid (as in Zygnema); zygospores ovoid,
quadrate-ovoid, or irregular, 24-30µ × 30-48µ, with rounded, retuse,
or produced angles; aplanospores unilaterally ovoid, 17-25µ × 20-40µ;
parthenospores 15-20µ × 20-30µ; median spore walls scrobiculate,
yellow-brown; akinetes with smooth heavy walls, 18-20µ × 20-30µ.
Type in herb, E. N. T. Collections No. 1177, 1939, 1949, 2686 and
2918. I have specimens from several localities in central Illinois;
Williamsport, Pa.; Minnesota; Mackinaw, Mich. and Kingston, Ontario.
This form is of great interest because of its resemblance, in the
vegetative condition, to _Zygnema decussatum_ (Vauch.) Transeau.
Also because it shows not only the zygospores, but aplanospores and
parthenospores. In all cases the secretion of cellulose accompanies
the process of spore formation. The unilaterally placed aplanospores
are strikingly different from those formed by the Zygnemas. In some
of the Illinois ponds it regularly produces only zygospores, in other
ponds from which I have collections covering a period of several
years it fruited only asexually, producing aplanospores and akinetes.
But several of the collections show all the forms of reproduction in
different cells of the same filament.
The characteristics of this species suggest that the peculiar _Zygnema
reticulatum_, which was described by Hallas in 1895[B], is in reality
a _Debarya_. The fact that the reproductive cells become filled with
cellulose, that the aplanospores are very irregular in form and that
the vegetative cells contain as high as seven chromatophores, are all
in harmony with this idea. On this basis it is also easy to understand
the most notable peculiarity of the species—that spores derived from
cells with several chromatophores produce two or three sporelings.
With the addition of the two new American species and this Danish
species =Debarya reticulata= (Hallas) nov. comb. the description
of the genus needs to be modified as follows:
Vegetative cells cylindrical or constricted at the ends, varying
from 1-16 diameters in length; chromatophore varying from an axile
plate with two or more pyrenoids to stellate chromatophores, each
with a central pyrenoid. Reproduction by zygospores formed of the
complete contents of the gametangia; not cut off from the gametangia
by partition walls; but in the process of conjugation, as the gametes
pass into the conjugating tube, their place is taken by a secretion of
cellulose. Aplanospores occupying only part of the sporogenous cell,
the remainder being filled with cellulose. All spores variable in form.
Parthenospores and akinetes occur not infrequently in some of the
species. The walls of the aplanospores and parthenospores resemble the
zygospores of the same species in their markings.
There are now eleven described species belonging to this genus. _D.
immersa_ W. West and _D. africana_ G. S. West bear a close resemblance
to _Mongeotia sphaerocarpa_ Wolle. _D. Hardyi_ G. S. West has much
the same appearance as _Mongeotia viridis_ (Kutz) Wittrock. _D.
desmidiodes_ W. & G. S. West, _D. calospora_ (Palla) W. & G. S. West,
_D. reticulata_, _D. americana_, and _D. decussata_ have characters
in common with the Zygnemas. _D. glyptosperma_ has the vegetative
characters common to several of the species, but its spores are quite
unique among the _Zygnemales_.
=ZYGNEMA= Agardh.
=Z. pectinatum= (Vauch.) Agardh.
This is probably common in the eastern half of the United States at
least. In Illinois along with the type occurs the variety _conspicuum_
(Hass.) Kirchner, and a variety with large spores. This latter variety
in fact is more common than the type.
var. =crassum= nov. var. Cellulis vegetativis 30-40µ × 20-80µ;
zygosporis 40-55µ × 50-60µ, ceterum ut in typo.
Vegetative cells 30-40µ × 20-80µ; zygospores 40-55µ × 50-60µ, otherwise
like the type. Type in herb. E. N. T. Collections No. 2350, 2392, 2660,
2685.
=Z. ericetorum= (Kütz) Hansgirg.
Professor G. S. West has studied the reproduction of this species and
finds that it is a true Zygnema and that the description and figure by
De Bary, which shows the cutting off of two special gametangia before
the union of the gametes is at fault, consequently there is no longer
any need of maintaining the genus _Zygogonium_ Kützing.
=Z. peliosporum= Wittrock.
Specimens of this species have been distributed under the name of _Z.
chalybeospernum_ Hansgirg, in P. B.-A. No. 808 from Boswell, Calif. (N.
L. Gardner); Amer. Alg. No. 156 from Ft. Collins, Colo. (J. H. Cowan);
and Amer. Alg. No. 392 from Vancouver, B. C. (J. E. Tilden). _Z.
chalybeospermum_ has the median wall smooth, but the spores of all of
the above specimens have distinctly scrobiculate median walls. In size
the specimens show a somewhat greater variation in dimensions than has
been recorded for European localities.
=Z. cruciatum= (Vauch) Agardh.
Specimens of this species have been found at Fath Pond, north of
Coffeen, Ill., in which both zygospores and aplanospores occurred in
abundance. The aplanospores fill or slightly enlarge the vegetative
cells as in _Z. Collinsianum_ Transeau,[C] but the ends of the spores
are usually more nearly truncate, 34-50µ × 30-80µ. At Casey, Ill., a
variety with the same dimensions but steel blue spores occurs in the
old Ice Plant Pond.
var. =caeruleum= nov. var. Cellulis vegetativis et sporis ut
in typo, sed membrana media sporarum caerulea.
Vegetative cells and spores as in the type, except that the
median spore wall is steel blue. Type in Collection E. N. T.
No. 495.
=Zygnema stellinum= (Müller) Agardh.
The specimen distributed under the name _Z. insigne_ (Hass.) Kütz. in
the P. B.-A. No. 457, from Chestnut Hill, Mass. (G. F. Moore), belongs
to this species as shown by the scattered mature spores. This species
is common everywhere in central Illinois. In the U. S. Natl. Herb, is a
specimen from Baltimore Co., Md., (J. D. Smith). In Amer. Alg. No. 157,
a specimen from St. Paul, Minn., (J. E. Tilden) shows both zygospores
and aplanospores. The aplanospores are cylindric ovoid in form,
occupying the entire cell 30-33µ × 40-88µ, median wall scrobiculate.
=Zygnema cylindricum= nov. sp.
Cellulis vegetativis 28-33µ × 28-66µ; zygosporis incognitis;
aplanosporis cylindricis vel tumido-cylindricis, 30-33µ × 24-58µ,
sporangia complentibus; membrana media brunnea scrobiculata.
Vegetative cells 28-33µ × 28-66µ; zygospores unknown; aplanospores
cylindric or tumid-cylindric, 30-33µ × 24-58µ, filling the sporangia,
median wall brown, scrobiculate. Type in Herb. E. N. T. No. 1164, 1177.
This species is not uncommon in ponds, and pools throughout central
Illinois. It was at first classified as aplanosporic material of _Z.
stellinum_ (Müller) Agardh. On going over the specimens in all my
collections, however, it was found that in no case were the filaments
containing the aplanospores connected with the filaments containing
zygospores. This must be the final test of the identity of the species,
as it occurs in some collections alone, sometimes associated only with
fruiting _Zygnema pectinatum_, and sometimes with _Z. stellinum_.
=Zygnema rhynchonema= Hansg.
In a collection of algae made at the Minnesota Seaside Station,
Vancouver Island, B. C., in 1901, by Professor Tilden, is a form which
perhaps belongs here. The vegetative cells are from 22-28µ in diameter,
and 32-52µ in length, while the European specimens are described as
16-20µ in diameter and 2-6 diameters long. The Vancouver specimens are
producing both aplanospores (globose, 24-26µ in diam.), and zygospores
(ovoid 24-28µ × 36-44µ) by the union of gametes through the partition
wall separating the two gametangia. The specimens show some evidences
of being in an abnormal condition.
=SPIROGYRA= Link.
=S. Juergensii= Kützing.
The specimen in P. B.-A. No. 510 from Knightsville, R. I., distributed
under the name of _S. longata_ (Vauch) Kütz. with cell diameter 27-30µ,
and ellipsoid spores 30-33µ in diameter, fertile cells enlarged,
evidently belongs to this species. The spores of _S. longata_ are
distinctly ovoid with rounded ends. In the Illinois specimens the
spores of _S. Juergensii_ frequently occur with diameters up to 33µ.
=S. varians= (Hass.) Kütz.
The varieties _scrobiculata_ Stockman and _minor_ Teodoresco have not
been reported from America. They both occur rarely in Illinois. The
latter I have also seen in material collected by Mr. Charles Bullard,
at Lynnfield, Mass. The former is characterized by its scrobiculate
spores, the latter by its smaller dimensions throughout. In my
herbarium _S. varians scrobiculata_ is represented in Collections No.
1799, and 1881; and _S. varians minor_ in Collection No. 2951.
=S. Borgeana= nov. sp.
Cellulis vegetativis 30-35µ × 50-200µ, dissepimentis planis,
chromatophoris singulis anfractibus arctis 1.5-5; cellulis
fractiferis altero latere inflatis, altero latere (in quo conjugatio
sequitur) rectis; zygosporis ellipticis, 33-40µ × 54-70µ, membrana
media flava, glabra.