EQUISETINEm, 



405 



period of vegetation, less often for several years. The sporangiferous spikes appear 

 either at the summit of these axes, which are at the same time the organs of assimi- 

 lation, or on special fertile shoots which, when destitute of chlorophyll and unbranched, 

 die after the dissemination of the spores [E. awense and Telmateid), or throw off 

 the terminal spike and act as vegetative shoots (.£. syl'vaticum and pratense). The 

 fertile axes are developed from the underground internodes of the erect vegetative 

 axes ; they remain during the summer, in which the latter are unfolded, in the bud- 

 condition beneath the ground, but during this period either develope their sporangi- 

 ferous spikes so far that in the next spring nothing is necessary except elongation and 

 the dissemination of the spores {E. ar'vense, pratense, Telmateia, &c.), or the spikes attain 

 their full development only in the spring after the elongation of the axes which bear 

 them {E. limosum). The habit of the aerial shoots is determined especially by the 

 number and length of the verticillate usually very slender lateral branches ; in some, 

 as E. hiemale, trachyodon, ramosissimum, and variegatum, they are generally entirely 

 wanting ; in others, as E. palustre and limosum^ they are few ; in others again, as E. ar- 

 'vense, Telmateia, and syl'vaticum, they are developed in large numbers. The height 

 of the leafy stem is in our native species mostly from i to 3 feet; in E. Udmateiay 

 where the ascending axis of the sterile shoots is colourless and destitute of chloro- 

 phyll, it attains a height of 4 or 5 feet and a thickness of about ^ inch ; while the green 

 slender leafy branches are even in this case scarcely § line thick. The tallest stems 

 are produced by E. giganteum in South America, as much as 26 feet high, but only about 

 the thickness of the thumb, and are kept in an upright position by neighbouring plants. 

 The Calam'ttes were as lofty, and as much as i foot thick. The rhizomes mostly creep 

 at a depth of from 2 to 4 feet beneath the ground, and extend over areas 10 to 50 feet 

 in diameter; but are also found at a much greater depth. They prefer damp, gravelly, 

 or loamy soil, their thickness varying from i to 2 lines to as much as ^ inch or more. 

 The surface of the internodes of the rhizome is, in some species, as E. Telmateia and 

 syl'vaticum, covered with a felt of brown root-hairs, which also clothe the leaf-sheaths of 

 the underground part of ascending stems, a peculiarity which reminds one of Ferns. 

 In some species, as E. limosum and palustre, the surface is smooth and shining, while in 

 others it is dull. The ridges and furrows of the aerial stems are usually but little de- 

 veloped on the underground stems ; sometimes the rhizomes are twisted. The central 

 canal of the internodes is sometimes wanting in the rhizomes ; but the lacunae of the 

 fibro-vascular bundles (carinal canals) and those of the cortical parenchyma (vallecular 

 canals) are always present ; the air which the tissues require and which is not found 

 in the usually very compact soil is carried by these canals from the surface to the 

 underground organs. As in the case of the spikes, the formation of the branches of 

 the leafy stems has already taken place entirely or at least to a great extent in the 

 preceding year in the underground bud, so that in the spring the internodes of the 

 ascending axis have only to extend and the slender lateral branches to unfold, as may be 

 seen with especial ease in E. Telmateia. All the more important cell-formations and the 

 processes of morphological differentiation thus take place underground ; the aerial un- 

 folding has for its main purpose only the dispersion of the spores and assimilation by the 

 leafy shoots, by the exposure of the cortex, which contains chlorophyll, to light. The 

 rapid growth of the upright stems in the spring is especially brought about by the simple 

 elongation of the internodal cells already formed, although permanent intercalary growth 

 of the internodes sometimes also takes place, and especially at their base within the 

 sheaths. The tissues often remain there for a long time in the young state, and in E. 

 hiemale the shorter internodes grow out of their leaf-sheaths after passing through the 

 winter, and they are then lighter in colour ; the shorter they were before the winter, 

 the more they elongate afterwards. 



Special Organs for Fegetati-ve Propagation, like those of Mosses, are not found in the 

 Equisetaceai any more than in Ferns ; but every part of the rhizome, and the under- 

 ground nodes of ascending stems, are adapted for the production of new stems. ^ In 



