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The crystals have very perfect cleavage parallel to the base and the rhombohedrong. They are very flexible and care must be used in handling them before measurement. Pittings on the basal pinacoid are trisymmetric with the lines of symmetry meeting at angles of 120°.
Examined under the polarizing microscope basal sections of these crystals appear isotropic and afford no interference figure. Sections parallel to the prism exhibit very weak double refraction. In sections 2mm. in thickness the double refraction is faintly perceptible without the use of a quartz plate. In sections 3mm.in thickness the double refraction is easily determined with use of the quarter undulation mica place. A considerable number of sections were tested and all were found to be negative. In these sections the interference color only reaches the yellow of the first order when the corresponding axes of the crystal and the mica plate are parallel. These characters therefore agree well with those determined for this substance by Traube. The borneol prepared from Abies balsamia is optically identical with this.
Isoborneol from Turpentine. As already stated, the symmetry of this substance is the same as that of borneol and the axial ratio is also so nearly identical that the measurements afforded essentially the same results. The determined axial ratio c= 0.93 of borneol is therefore assumed for this substance. The observed forms on the normal type of crystals are: C, op (0001); 8, 3R (3031); 9, -8R (8051); m, a P (1010); and e, -4R (4011). A crystal of this type is represented in figure 2. The above forms were determined by the following measurements : Measured. Average.
90 08 ene, 75 10 75 10
77 11 The crystals of this substance possessing rhomboidal habit represent quite a different crystal combination from the normal type of crystals. The prominent forms on these crystals (after the base) are the rhombohedron x, R (5053) and the prism m, o P (1010). Quite frequently the former appears forming two opposite sides of the rhomboid, the other two sides being formed by the prism alone (see figure 3). The form a may be the one from which Traube determined the axial ratio
of this substance. Determined from the writer's measurements of the position of this plane the axial ratio would be (considering it the fundamental rhombohedron) c = 1.589, Traube's value being c=1:41. The observed forms comprising this combination are: c, oP (0001); X, R (5053); m, o P (1010); t, GR (2023); 2, 5R (5051); and e, -4R (4011). The forms y, 1R and r, R (or 1R) were also observed on one crystal but their sign was not deterinined. The above forms were identified by means of the following measurements:
SR, 47 3
TIR, 49 32 As regards color, enclosures, and cleavage, isoborneol seems to differ but little from borneol. The great difference between the two substances is seen when they are examined in prismatic sections in parallel polarized light. A section of borneol in which double refraction is not perceptible, would if prepared from isoborneol yield yellow of the first order. Sections of isoborneol 2mm, in thickness yield, when the interference of the crystal is added to that of the quarter undulation mica plate, violet of the second order, whereas similar sections of borneol yield under the same conditions yellow of the first order. The optical character has been tested on a considerable number of crystals and found to be always negative. The substance examined by Traube is reported to be positive.
In conclusion I would express my thanks to Professor Edward Kremers and Mr. Carl G. Hunkel of the Department of Pharmacy, University of Wisconsin, for supplying me with the material studied.
Mineralogical Petrographical Laboratory, University of Wisconsin.
Art. XXXVIII.-Synopsis of the Mode of Growth and
Development of the Graptolitic Genus Diplograptus ;* by R. RUEDEMANN.
The main results of the observations made upon a large collection of specimens of the genus Diplograptus found near Dolgeville, N. Y., are the following:
(1) Diplograptus pristis Hall (= D. foliaceus Murch. sp.) and Diplograptus pristiniformis Hall (= D. dentatus Brgt. sp.), two typical graptolites of the Utica shale, which were hitherto known to grow only in single stipes, have been found growing in compound colonial stocks which appear in the fossil state as stellate groups. The compound fronds of D. pristis Hall reach a diameter of four inches and are composed in some specimens of as many as forty stipes, those of D. pristiniformis Hall are only an inch in diameter and have about a dozen of stipes.
(2) The virgulæ are joined to a central cornecting stem, the “funicle” of Hall, which is mostly extended to a vesicle of quadrangular shape. The funicle is inclosed in a thick chitinous capsule, which is identical with the central disc” of the compound fronds of numerous Monograptide. The central disc, too, is drawn out at the four corners where most of the virgulæ leave, so as to appear .subquadrangular in the compressed state.
(3) The central disc is surrounded by a verticil of oval capsules, which number from four to eight and probably still more. The latter appear mostly as oval impressions ; in a few specimens a thin chitinous film is discernible; in some fossils, however, the oval appendage is made up of distinct siculæ which radiate from an axial club-shaped protuberance within the vesicle, to which they are joined by the filiform prolongation of their pointed ends. The mature siculæ are found near the base, the younger ones toward the top of the vesicle. The section of the test of the vesicle appears sometimes as a chitinous ring.
The enclosed siculæ give evidence that the vesicles were organs of reproduction which are to be compared with the “gonangia ” of recent hydrozoa. In some specimens the compound frond is surrounded by a dense crowd of siculæ, most of which are pointing with the broad ends outwards, so as to make it obvious that they took their origin in the center of the · frond. In this case the gonangia were apparently opened shortly before the covering of the fossil.
* Abstract of a paper on the genus Diplograptus to be published in the Report of the State Geologist of New York for the year 1894.
In this that the with the
(4) The majority of the fossils present a large subquadratic impression which overlaps the gonangia, and sometimes even the proximal ends of the stipes. Some specimens of D. pristiniformis Hall, found in a limestone-layer which is interpolated in the shale, reveal the fact that this impression belongs to an organ which was made up of a large spherical segment on the upper side and a smaller one on the under side of a quadrangular plate. The latter has a system of furrows parallel to the margin. The author compares the whole organ with the air-bladder or pneumatocyst of the Discoidere, a family of the Siphonophorae, on account of its size, its being the topmost organ, and on account of the apparent absence of any structure-besides the furrowing in the plate which reminds much of the system of canals in the float of the Discoideæ.
We may infer from the preceding observations that the colonial stock was carried by a large air-bladder, to the underside of which was attached the funicle. The latter was enclosed in the central disc and this was surrounded by a verticil of vesicles, the gopangia, which produced the siculæ. Below the verticil of gonangia and suspended from the funicle was the tuft of stipes.
(5) A close observation of the siculæ, which are found so numerously on the slabs, detected the fact that the siculæ, at the time of developing the first two hydrothecæ, possessed a quadrangular plate, joined by a small node in the center to the end of the filiform proximal process. On young stipes with seven hydrothecæ on one side and six on the other, can be already discerned four oval, distinctly furrowed impressions around the central node.
The first appearing quadrangular plate—or probably vesicle -develops into the pneumatocyst, the central node into the funicle and central disc; and in the small oval impressions we most probably see the budding gonangia. The sicula, therefore, which grows out to the primary stipe develops first the floating organ and then the central organs.
It deserves to be noted that the new hydrothecæ of the primary stipe sprout in the direction towards the central organs while the sicula remains in all stages of development at the opposite end of the central organs, i.e., at the distal end.
Whether the primary stipe produces first new siculæ, some of which remain in connection with the center, forming new stipes and by these the compound frond, or whether other detached siculæ gain connection with the new center of the first stipe, could not be decided. The fact, however, is that fronds with one full-grown stipe, the primary one, and several young ones are a rather common occurrence, further that fronds have been found to the center of which siculæ without
any hydrothecæ and stipes in all stages of development were joined.
(6) A most astonishing feature of the compound fronds is the position of the siculæ at the remote end of the stipes, so that the so-called “proximal ” sicula-bearing end of the single stipes appears in the compound colonial stock as the distal one. This is accounted for by the observation that the first hydrothecæ of each stipe sprout at the distal, broad end of the sicula and that all following hydrothecæ make their appearance more proximally. The stipe, therefore, is growing backward, towards the center, or like a leaf at the base, and the sicula is carried to the distal end.
(7) By the possession of a pneumatocyst and the arrangement of the reproductive organs at the bases of the stipes, the colonial stocks of Diplograptus had a general similarity to those of certain Siphonophorce, while the chitinous structure of the hydrothecæ and gonangia can be only referred to the Sertularians. It thus becomes evident that the genus Diplograptus, like so many palæozoic fossils, has the combined properties of different groups, thus giving valuable hints in regard to the common ancestors of these groups.
EXPLANATION OF FIGURES.
the limestone. a. Pneumatocyst. b. Gonangium. Fig. 4.—Diplograptus pristis Hall. Enlarged four times.
a. Gonangium filled with siculæ.
c. Young stipe with distinct sicula at the distal end. FIG. 5.—Detached sicula of D. pristis Hall with pneumatocyst.