DR. SCOTT has recently been revising the catalogue of his

Transcription

1 i6 Mrs. D. H. Scott. ON THH MEGASPORE OP FOLIACEUS. LEPIDOSTROBUS BY RINA (MRS. D. H.) SCOTT, F.L.S, [WITH PLATE VIII. AND TEXT-FIGS 24, 25.] DR. SCOTT has recently been revising the catalogue of his collection of fossil plants from the coal measures and in looking through the slides one's eye gradually became impressed with the presence in many of the sections from Dulesgate and the Halifax hard bed of a curious looking, very badly preserved, black object, like a much crumpled spore with an appendage attached to it (Text-fig. 24, and Plate VIII., 1217).' It was not until 1325 slides had been searched, that I came to the conclusion, that this object was of the nature of a spore and worth investigating. I drew each specimen found with the camera lucida and became more and more convinced that it was really a megaspore and not, as one might easily think at first sight, a badly preserved petiole or stem. Also it soon became evident that the appendage was a definite structure, less altered in the course of preservation than the megaspore to which it belonged. I was strengthened in my opinion that it was a megaspore by finding a specimen (Plate VIII., 1490) in a sporangium, though the appendage was not shown. Up to the present, I have found over 40 specimens in 1500 slides, so that it may be looked upon as a fairly common object; I hope that the megaspores drawn on Plate VIII may help others to find fresh examples (Plate VIII) appears to possess two appendages, this I think is due to the twisting of the megaspore so that one part of the appendage is cut at right angles to the other. I had temporarily given tlie name of Triletes diabolicus to this specimen: Triletes being the general name used by Mr. Kidston for megaspore and diabolicus explains itself when one has seen the object. Let us now examine the megaspore in more detail. It is not easy to decide whether it was spherical or egg-sliaped, but on measuring round the outline of a camera lucida drawing with thread, I find that the diatiieter of a sphere would be about 1"5 mm. ' The numbers given in coiiiicctioti with the figures ace the cabinet numbers of the slides in Dr. Scott's collection.

2 On the Megaspore of Lepidostrobus foliaceus. 117 From such measurements as it has been possible to make, there were probably several, perhaps four, megaspores in each sporangium. Turning to the appendage it seems clear, that in Plate VIII., 1719 and 1217, where the veins are radiating out from the point of attachment, are sections through the appendage in one direction. Fig, 24. Photographof 1217 (Plate VIII.) while 1539, 1343 and 1715 are cut at a plane at right angles to the former, and tbe veins are cut vertically. In 1715 there appears to be a cleft filled by hairs, which may be where the microspores gained access to the megaspore. In 1887, a much less well-preserved specimen, there are microspores in the cleft. At a, a, these microspores are shown enlarged. 1 have made a model of tbe appendage and spore, wbich appears to explain the appearance of tbe difl'erent sections. It reminds one of the so-called " swimming-apparatus" of Azolla. The appendage was evidently a fairly substantial structure, which resisted distortion much better tban the megaspore itself. The nature of the structure cannot be determined, but it is not cellular and its appearance indicates, that it was part of the cell-wall probably derived from tbe tapetal protoplasm. Tbere is some evidence of tbis origin in the case of the bristles of other megaspores. While examining Lepidostrobus foliaceus, further details of which will be found in Mr. Maslen's' paper on Lepidostrobus, I came across megaspores of this plant in their sporangium in connection with the characteristic bract (Plate VIII., 5 and 1403 and Text-fig. 25). Tbis point is of especial interest as up till now the cone has always been considered homosporous^ We must turn to Professor Williamson's splendid specimen of ' On the Structure of Lepidostrobus. Trans, of the Linnean Society. Vol. V. 1899, P. 373, Plate 38, Figs On the Organization of the Fossil Plantsof the Coal-Measures, Part XIX. Phil. Trails. Royal Society, Series B. 1893, P, 27, Plate 9, Fig. 57.

3 118 On the Mcgaspore of I.epido.strobus foliaceus. the microsporangiate cone of this plant in order to understand the details of its structure. Tbe original slide is in the Natural History Museum, C.N Tbis is the type specimen on which Mr. Fig. 25. Photograph of 5 (Plate VIII.) Sporangia containing megasporcs, one with the characteristic bract oi Lcpiitostrobus fotiaccus. m., mcgaspore. mg., mcgasporangium. h., bract. Maslen founded his species Lepidostrobus foliaceus. The section is a fairly radial one through tbe microsporangiate part of the cone. It is not quite median but it clearly sbows tbe elongated form of the sporangia seated on the sporopbylls with tbeir leaf-like laminae from which tbe specific name was taken. We bave been tryinjj for the last year to sort out tbe different megaspores of Lcpidostrobns, so I looked through our camera lucida drawings of megasporcs to match those found in tbe sporangia. The result was, tbat the only ones at all corresponding in size and texture were my otber new megasporcs Triletes diabolicus. I searched carefully to see if 1 could find any sign of tbe curious appendage, but without success, till when 1778 was reached I had the good fortune to find a sporangium containing a typical Triletes diabolicus. Since then I bave been tbrougb every slide of Lepidostrohus foliaceus and have found that 25 out of 36 show tbe Triletes. 1 now thought if the type cone of Williamson were examined and showed Triletes diabolicus in the cone the evidence would be conclusive. Tbe cone, however, so far as shown, is purely microsporangiate, but the section shows a very fine specimen of Triletes diabolicus completely enclosed in a sporangium, identical in appearance witb those containing the microspores, so that I think tbere is little doubt that the two new megaspores are really one and the same, that the Williamson cone must in future be considered as a heterosporous not a bomosporous one and tbat Triletes diabolicus must disappear and become the megaspore of Lepidostrobus foliaceus.

4 Apical Meristems oj the Roots of Monocotyledons. 119 I am indebted to Mr. L. A. Boodle for the photographs reproducee in Figa. 24 and 25. The Figures on Plate VIII. are from my own drawings. DESCRIPTION OF FIGURES ON PLATE VIII., ILLUSTRATING MRS. D. H. SCOTT S PAPER "ON THE MEGASPORE OF LEI'iDosriionus FOI.IACEUS.'' Dr-awings of mcgasporcs of Lefiulnsfrolms /ohaccus, sliowing the appendage. The numhers are those of the slides in Dr. Scott's eollection shows a mcj;aspore in a sporati},'iuin. 5 is represeiitei-l in the photofjr.iph Fi}^ is i-cprcsented in the photojjraph Fi^. 24. THE APICAL MERISTEMS OF THE ROOTS OF CERTAIN AQUATIC MONOCOTYLEDONS, BY DAISY G. SCOTT, B.SC. (Univcl'sity of Liverpool). [PLATE IX.] THE mode of origin of the permanent tissues from the apical meristem in the root of the Monocotyledon has been the subject of investigation at the hands of many anatomists. The results arrived at have been summarised more especially by two authorities, viz. : by De Bary in his " Vergleichende Anatomie der Vegetationsorgane der Phanerogamen und Farnen," 1877, (English Edition, 1884), and by Van Tieghcm in " L'origine des membres endogenes," These views may be expressed briefly as follows : De Bary considers that there are two types of structure in the apices of the roots of Monocotyledons: (a), a type found in very few Monocotyledons, in which there are four initial layers giving rise respectively to (1) the plerome, (2) the periblem, (3) the der. matogen, and (4) the calyptrogen and (b), a type found in the majority of Monocotyledons, in which there are three sets of initials giving rise respectively to (1) the plerome, (2) the periblem and dermatogen together, (3) the calyptrogen. De Bary further holds that the epidermis is always a single layer, and that this layer originates separately or from a common group with th2 periblem. Van Tieghem, with but few exceptions, considers that the mode

5