Fig. 108.—Transverse Section of Young Root of Calamites
w, Wood of axis; l, spaces in the lacunar cortex, whose radiating strands r are somewhat crushed; ex, outermost cells of cortex with thickened wall.
Fig. 109.—Diagram of Cone of Calamites
A, Main axis; br, sterile bracts; sp, sporophylls with four sporangia S attached to each, of which two only are seen.
The young roots of these plants have a very characteristic cortex, which consists of cells loosely built together in a lacelike fashion, with large air spaces, so that they are much like water plants in their appearance (see [fig. 108]). Indeed, so unlike the old roots and the stems are they, that for long they were called by another name and supposed to be submerged stems, but their connection with Calamites is now quite certain. As their woody axis develops, the secondary tissue increases and pushes off the lacelike cortex, and the roots become very similar in their anatomy to the stems. Both have similar zones of secondary wood, but the roots do not have those primary canals which are so characteristic of the stems, and thereby they can be readily distinguished from them.
The fructifications of the Calamites were not unlike those of the living types of the family, though in some respects slightly more complex. Round each cone axis developed rings of sporophylls which alternated with sterile sheathing bracts. Each sporophyll was shaped like a small umbrella with four spokes, and stood at right angles to the axis, bearing a sporangium at each of the spokes. A diagram of this arrangement is seen in [fig. 109].
Fig. 110.—Longitudinal Section of Part of Calamites Cone
br, Sterile bracts attached to axis; sp, attachment of sporophylls; S, sporangia. At X a group of four sporangia is seen round the sporophyll, which is seen at a. (Microphoto.)