First in the Permian we meet with the important genus of plant called _Calamites_, which were very abundant in the Coal Measures. Many of the Calamites were of great size, for specimens with large trunks have been found 30 ft. and more long, which when growing must certainly have been much taller than that. The number of individuals must also have been very great, for casts and impressions of the genus are among the commonest fossils. They were, in fact, one of the dominant groups of the period. Like the Lycopods, the Equisetaceæ reached their high-water mark of development in the Carboniferous period; at that time the plants were most numerous, and of the largest size and most complicated structure that they ever attained. [Illustration: Fig. 104.—Small Branches attached to stouter Axis of _Calamites_. Photo of Impression] As will be immediately suspected from analogy with the Lycopods, they differed from the modern members of the family in their strongly developed anatomy, and in the strength and quantity of their secondary wood. Yet in their external appearance they probably resembled the living genus in all essentials, and the groves of the larger ones of to-day growing in the marshes probably have the appearance that the palæozoic plants would have had if looked at through a reversed opera glass. Fig. 104 is a photograph of some of the small branches of a Calamite, in which the ribbed stem can be seen, and on the small side twigs the fine, pointed leaves lying in whorls. In most of the fossil specimens, however, particularly the larger ones, the ribs are not those of the true surface, but are those marked on the _internal cast_ of the pith. [Illustration: Fig. 105.—Transverse Section of _Calamites_ Stem with Secondary Wood _w_ formed in Regular Radial Rows in a Solid Ring _c_, Canals associated with the primary bundles; _p_, cells of the pith, which is hollow with a cavity _l_, _cor_, Cortex and outer tissues well preserved. (Microphoto.)] Among tissue petrifactions there are many Calamite stems of various stages of growth. In the very young ones there are only primary bundles, and these little stems are like those of a living Equisetum in their anatomy, and have a hollow pith and small vascular bundles with canals associated. The fossil forms, however, soon began to grow secondary wood, which developed in regular radial rows from a cambium behind the primary bundles and joined to a complete ring.