EQUISETIN^E. 363 



The bundles vary considerably as to the tissues they contain, 

 but they generally possess tracheary and sieve tissues ; the 

 former is usually well-developed as spiral, scalariform, or 

 pitted. Sieve tissue is, as a rule, not so well developed as 

 the former, consisting for the most part of thin-walled, 

 elongated cells, in which the characteristic sieves are less 

 regularly formed. Fibrous tissue occurs only to a limited 

 extent as a constituent of the fibro- vascular bundles. Paren- 

 chyma is also found in them, but, like the former, it is 

 usually not abundant. The fundamental system of tissues 

 includes various forms of parenchyma and sclerenchyma ; 

 ihe latter, however, is frequently wanting. Collenchyma and 

 laticiferous tissue are not found in the greater part of the 

 Division ; but the former occurs in Marattiaceae, in which or- 

 der, according to Sachs' observations, there are also indica- 

 tions of a rudimentary laticiferous tissue. 



I. CLASS EQUISETIJSLE. 



473. In the plants of this class the plant-body (of the 

 asexual generation) consists of a hollow elongated and jointed 

 -axis, bearing upon each node a whorl of narrow united leaves, 

 which form a close sheath (s, Fig. 249) ; the stem is always 

 grooved or striate, and is usually rough and hard from the 

 large amount of silica deposited in the epidermis. The 

 branches arise by the side of the axils of the leaves consti-. 

 tuting the sheaths, and consequently they are in whorls. 

 Both the main axis and the branches are in most cases richly 

 supplied with chlorophyll-bearing parenchyina ; in some of 

 the species (e.g., Equisetum Telmateia and E. arvense) the 

 stems which bear the spores are destitute of chlorophyll. 

 All the species develop numerous colorless branching under- 

 ground stems, which bear roots and rudimentary sheaths, 

 and which each year send up the vegetating and spore- 

 bearing stems. Both root and stem grow from an apical cell. 



474. In common with most members of tlrs division^ 

 the Equisetinse are perennial plants. In some species the 

 underground portions only persist, the aerial stems dying at 

 the end of each year, as is the case in E. Telmateia, E. arvense, 



