EQUISET1NEAE. 36 



the dispersion of the spores, as in K. Telmaieja and E. arvense, or, as in E. syh'aticnm 

 and E.pratense, throw off the fertile head and continue to live as vegetative shoots. The 

 fertile axes are developed from the underground internodes of ascending vegetative 

 axes ; during the summer in which the latter are unfolded above ground the fertile 

 shoots remain in the bud state beneath the ground, but they form their sporangia in this 

 state, either so completely that in the next spring they have only to elongate their.stems 

 and disperse their spores, as is the case in E. arvense, E.pratense, E. Telmateja and 

 others, or the spikes do not complete their development till after the elongation of the axes 

 which bear them in the spring (E. limositm]. The outward appearance of the aerial 

 shoots depends chiefly on the number and length of their whorled and usually very slender 

 lateral branches, which in some species, as E. trachyodon, E. ramosissimitm, E. Jiiemale, 

 E. variegatiim, are as a rule entirely wanting, in others, as E. pain stre and E. liinosum, 

 are somewhat scanty, in others again, as E. arvense, E. Telmateja, and E. sylvaticum, are 

 developed in great abundance. The height of these leafy stems is in our native species 

 usually from one to three feet ; in E. Telmateja the ascending axis of the sterile 

 shoot, which is without chlorophyll and colourless, reaches a height of from four to 

 five feet with a thickness of about half an inch, while the slender leafy branches are 

 scarcely half a line in thickness. The tallest stems are those of E. giganteum from 

 South America ; these may be as much as twenty-six feet high, but are only about the 

 thickness of a thumb and are kept in an upright position by the neighbouring plants ; 

 the Calamites must have been as tall, and sometimes a foot thick. The rhizomes 

 generally run at a depth of from two to four feet beneath the surface and spread over 

 spaces of from ten to fifty feet in diameter, but they are sometimes found at much 

 greater depths ; they prefer wet gravelly or loamy soil ; their thickness varies from one 

 or two lines to half an inch or more. The surface of the internodes in the rhizome of 

 many species (E. Telmateja, E. sylvaticum, etc.) is covered with a felt of brown root- 

 hairs ; a similar covering is found on the foliar sheaths of even the underground parts of 

 ascending stems, and in this point there is a resemblance to the Ferns ; in other species, 

 as E. palustre and E. liinosum, the surface is smooth and shining or in others again dull. 

 The ridges and furrows characteristic of the aerial stems are generally less developed 

 on the underground stems, which are sometimes perfectly smooth. The internodes 

 of the rhizomes are not always hollow, but the lacunae of the vascular bundles (carinal 

 canals) and those of the cortical parenchyma (vallecular canals) are always present, for 

 they serve to convey the needful air, which is not to be obtained in the usually compact 

 soil, from the surface to the organs underground. The branches of the leafy stem, like 

 the fructifications, are also formed either wholly or to a great extent in the underground 

 bud in the course of the preceding year, so that only the elongation of the internodes 

 of the ascending axis and the unfolding of the slender lateral branches remain to take 

 place in the spring; the process may be easily observed in E. Telmateja. It follows 

 that all the more important cell-formations and the processes which result in the mor- 

 phological differentiation of the plant are accomplished underground ; the unfolding in 

 the air has for its chief objects the dispersion of the spores and assimilation by means 

 of the chlorophyll in the cortical tissue of the leafy shoots when exposed to the light. 

 The rapid elongation of the erect stems in spring is chiefly due to simple increase in 

 length of the cells of the internodal tissue already formed, but permanent intercalary 

 growth of the internodes sometimes occurs at their base inside the sheaths, where the 

 tissues often continue for a long time in the young state ; in this way the internodes in 

 E. hiemale which are still short and of a lighter colour grow out of their sheaths when 

 the winter is over, and the shorter they were before the winter, the more do they 

 afterwards increase in length. 



Special organs for vegetative propagation, such as are known in the Mosses, are not 

 found in the Equisetaceae any more than in the Ferns ; but instead of these every piece 

 of rhizome and the underground nodes of ascending stems are adapted for the pro- 

 duction of new plants. In some species underground shoots swell out into tubers of 



