The sporangia of Hyphochytrium infestans[426], as figured by Fischer in Rabenhorst’s work bear a close resemblance to those of the fossil. It would seem very probable that Renault’s species may be reasonably referred to the Chytridineae, as he proposes.
Fig. 43. 1. Oochytrium Lepidodendri, Ren. (After Renault.) 2. Polyporus vaporarius Fr. var. succinea. (After Conwentz.) 3. Cladosporites bipartitus Fel. (After Felix.) 4. Haplographites cateniger Fel. (After Felix.)
Peronosporites antiquarius W. Smith. Fig. 41, E.
In an address to the Geologists’ Association delivered by Mr Carruthers in 1876 a brief reference, accompanied by a small-scale drawing, is made to the discovery of a fungus in the scalariform tracheids of a Lepidodendron from the English Coal-Measures[427]. In the following year Worthington Smith published a fuller account of the fungus, and proposed for it the above name[428], which he chose on the ground of a close similarity between the mycelium and reproductive organs of the fossil form and recent members of the Peronosporeae. In Smith’s description the mycelium is described as bearing spherical swellings containing zoospores. These spherical organs are fairly abundant and not infrequently met with in sections of petrified plant-tissues from the English Coal-Measures; they may be oogonia or sporangia, or in some cases mere vesicular expansions of a purely vegetative hypha. No confirmation has been given to the supposed spores referred to by Smith. Prof. Williamson and others have carefully examined the specimens, but they have failed to detect any trace of reproductive cells enclosed in the spherical sacs[429]. The mycelium does not appear to show any satisfactory evidence of its being septate as figured by Smith.
The example shown in fig. 41 E has been drawn from one of the Williamson specimens: it illustrates the form and manner of occurrence of the characteristic swellings. It is probable that some at least of the vesicles are either sporangia or oogonia, but we cannot speak with absolute confidence as to their precise nature. The general habit and structure of the fungus favour its inclusion in the class of Phycomycetes. The occurrence of several of the vesicles close together on short hyphal branches, as shown in Williamson’s figures, suggests the spherical swellings on vegetative hyphae, but it is impossible to speak with absolute confidence. There is a close resemblance between this English form and one recently described by Renault as Palaeomyces gracilis Ren.[430]; the two fossils should probably be placed in the same genus.
The examples referred to below and originally recorded by Cash and Hick no doubt belong to the same type as Smith’s Peronosporites.
The sketches reproduced in fig. 44 have been drawn from specimens originally described by Cash and Hick in 1878[431]. The sections were cut from a calcareous nodule from the Halifax Coal-Measures containing fragments of various plants and among others a piece of cortical tissue, probably of a Lepidodendron or Stigmaria. In a transverse section of this tissue one sees under a moderately high power that the cells have become partially separated from one another by the destruction of the middle lamellae (fig. 44 A). The cell-cavities and the spaces between the isolated cells contain numerous fine fungal hyphae, which here and there terminate in spherical swellings. One such swelling is shown under a low power in fig. 44 A, in the middle uppermost cell, and more highly magnified in fig. 44 B. In fig. C there are two such swellings (the larger one having a diameter of ·003 mm.) in contact, but the connection does not appear to be organic. The cell-walls of the infected tissue present a ragged and untidy appearance, and in places (e.g. fig. 44 D) the membrane has been pierced by some of the mycelial branches.
Fig. 44. Cells with fungal hyphae. A. A piece of disorganised tissue, showing the separation of the cells. B. Part of A more highly magnified. C. A single cell containing two swollen hyphae. D. Partially destroyed cell-membranes pierced by fungal hyphae. (Drawn from sections in the Edinburgh Botanical Museum, originally described by Cash and Hick.)