[AK] Or, as they have recently been named by some botanists, "Heterosporous Filices," though they are certainly not ferns in any ordinary sense of that term.
My attention was first directed to these organisms by the late Sir W. E. Logan in 1869. He had obtained from the Upper Erian shale of Kettle Point, Lake Huron, specimens filled with minute circular discs, to which he referred, in his report of 1863, as "microscopic orbicular bodies." Recognising them to be macrospores, or spore-cases, I introduced them into the report on the Erian flora, which I was then preparing, and which was published in 1871, under the name _Sporangites Huronensis_.
[Illustration: Fig. 15.--Vegetation of the Devonian period, restored. _Calamites_, _Psilophyton_, _Leptophleum_, _Lepidodendron_, _Cordaites_, _Sigillaria_, _Dadoxylon_, _Asterophyllites_, _Platyphyllum_.]
In 1871, having occasion to write a communication to the "American Journal of Science" on the question then raised as to the share of spores and spore-cases in the accumulation of coal, a question to be discussed in a subsequent chapter, these curious little bodies were again reviewed, and were described in substance as follows:
"The oldest bed of spore-cases known to me is that at Kettle Point, Lake Huron. It is a bed of brown bituminous shale, burning with much flame, and under a lens is seen to be studded with flattened disc-like bodies, scarcely more than a hundredth of an inch in diameter, which under the microscope are found to be spore-cases (or macrospores) slightly papillate externally (or more properly marked with dark pores), and sometimes showing a point of attachment on one side and a slit more or less elongated and gaping on the other. When slices of the rock are made, its substance is seen to be filled with these bodies, which, viewed as transparent objects, appear yellow like amber, and show little structure, except that the walls can be distinguished from the internal cavity, which may sometimes be seen to enclose patches of granular matter. In the shale containing them are also vast numbers of rounded, translucent granules, which may be escaped spores (microspores)." The bed containing these spores at Kettle Point was stated, in the reports of the "Geological Survey of Canada," to be twelve or fourteen feet in thickness, and besides these specimens it contained fossil plants referable to the species _Calamites inornatus_ and _Lepidodendron primævum_, and I not unnaturally supposed that the Sporangites might be the fruit of the latter plant. I also noticed their resemblance to the spore-cases of _L. corrugatum_ of the Lower Carboniferous (a Lepidodendron allied to _L. primævum_), and to those from Brazil described by Carruthers under the name _Flemingites_, as well as to those described by Huxley from certain English coals, and to those of the Tasmanite or white coal of Australia. The bed at Kettle Point is shown to be marine by its holding the sea-weed known as _Spirophyton_, and shells of _Lingula_.