3 74 VASCULAR CRYPTOGAMS. 



has not yet become split up into elaters, but \vhich already show the corresponding 

 differentiations {D, E), are allowed to lie for some time in glycerine, the spore 

 contracts considerably, surrounded by its inner coat, while the second cuticu- 

 larised coat raises itself from the former in folds. The inner coat is differentiated into 

 an outer granular cuticularised exospore, and an inner endospore of cellulose. 



Very little need be said about the Classification of Equisetaceae, as all existing forms 

 are so nearly related to one another that they may be included in a single genus, Equi- 

 setum. Even the Equisetaceae of earlier geological periods, the Calamites, show, in the 

 little that is still discernible of their organisation, the closest agreement with existing 

 forms. 



The Habit of the Equisetaceae is, like their morphological structure, of a very 

 characteristic kind. In all the plant is perennial by means of creeping underground 

 rhizomes, from which ascending aerial shoots rise annually, mostly lasting only for one 

 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. ar-vense and Telmateia'), or throw off 

 the terminal spike and act as vegetative shoots {E. syhmticum 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, Sec), 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 £. hyemale, trachyodon, ramosissimum, and imriegatum, they are generally entirely 

 \vanting ; in others, as E. palustre and limosum, rather few, in others again, as E. ar~ 

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

 of this leafy stem is in our native species mostly from i to 3 feet ; in E. Telmateia^ 

 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 Galamites 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 deve- 

 loped on the underground stem.s ; 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 under- 

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

 leafy stems has already commenced entirely or at least for the greater part in the 

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



