Fig. 116.—Diagram of Arrangement of Scales and Sporangia in Cones of Sphenophyllum
A, Axis; br, bract; S, sporangium, with stalk st.
In its anatomy the stalk of the cone has certain features similar to those in the stem proper, which were among the first indications that led to the discovery that the cone belonged to Sphenophyllum. There were numerous spores in each of the sporangia, which had coats ornamented with little spines when they were ripe ([fig. 117], if examined with a magnifying glass, will show this). Hitherto the only spores known are of uniform size, and there is no evidence that there was any differentiation into small (male) and large (female) spores such as were found in some of the Lepidodendrons. In this respect Sphenophyllum was less specialized than either Lepidodendron or Calamites.
In the actual sections of Sphenophyllum cones the numerous sporangia seem massed together in confusion, but usually some are cut so as to show the attachment of the stalk, as in [fig. 117], st. As the stalk was long and slender, but a short length of it is usually cut through in any one section, and to realize their mode of attachment to the axis (as shown in [fig. 116]) it is necessary to study a series of sections.
Fig. 117.—Part of Cone of Sphenophyllum, showing sporangia sp, some of which are cut so as to show a part of their stalks st. B, Bract. (Microphoto.)
Of the other plants belonging to the group, Bowmanites Römeri is specially interesting. Its sporangia were borne on stalks similar to those of Sphenophyllum, but each stalk had two sporangia attached to it. Two sporangia are also borne on each stalk in S. fertile. These plants help in elucidating the nature of the stalked sporangia of Sphenophyllum, for they seem to indicate a direct comparison between them and the sporophylls of the Equisetales.
There is, further, another plant, of which we only know the cone, of still greater importance. This cone (Cheirostrobus) is, however, so complex that it would take far too much space to describe it in detail. Even a diagram of its arrangements is extraordinarily elaborate. To the specialist the cone is peculiarly fascinating, for its very complexity gives him great scope for weaving theories about it; but for our purposes most of these are too abstruse.
Fig. 118.—A, Diagram of Three-lobed Bract from Cone of Cheirostrobus. a, Axis; br, the three sterile lower lobes of the bract; sp, the three upper sporophyll-like lobes, to each of which were attached four sporangia S. B, Part of the above seen in section longitudinal to the axis. (Modified from Scott.)