Among living plants the fine rootlike rhizophores of Selaginella bear some resemblance to Stigmaria in essentials, though so widely different from them in many ways, and they are probably the closest analogy to be found among the plants of to-day. The individual cells, we have already seen, are strikingly similar in the case of fossil and living plants. There are, of course, specific varieties peculiar to the fossils, of which perhaps the most striking seem to be some forms of _hair_ cells. For example, in a species of fern from the French rocks there were multicellular hairs which looked like little stems of Equisetum owing to regular bands of teeth at the junctions of the cells. These hairs were quite characteristic of the species—but hairs of all sorts have always abounded in variety, so that such distinction has but minor significance. [Illustration: Fig. 48.—Stele of _Lepidodendron_ W, surrounded by a small ring of secondary wood S] As was noted in the table (p. 58) the only cell types of prime importance which were not evolved by the Palæozoic plants were the wood vessels, phloem and accompanying cells which are characteristic of the flowering plants. Among the fossils the vascular arrangements are most interesting, and, as well as all the types of stele development noted in the previous chapter as common to both living and fossil plants, there are further varieties found only among the fossils (see fig. 50). The simple protostele described (on p. 61) is still found, particularly in the very young stages of living ferns, but it is a type of vascular arrangement which is not common in the mature plants of the present day. In the Coal Measure period, however, the protostele was characteristic of one of the two main groups of ferns. In different species of these ferns, the protostele assumed a large variety of shapes and forms as well as the simple cylindrical type. The central mass of wood became five-rayed in some, star-shaped, and even very deeply lobed, with slightly irregular arms, but in all these cases it remained fundamentally monostelic. Frequently secondary tissue developed round the protosteles of plants whose living relatives have no such tissue. A case of this kind is illustrated in fig. 48, which shows a simple circular stele surrounded by a zone of secondary woody tissue in a species of _Lepidodendron_. [Illustration: Fig. 49.—_Lepidodendron_, showing Part of the Hollow Ring of Primary Wood W, with a relatively large amount of Secondary Tissue S, surrounding it]