202 PRACTICAL BOTANY. 



may be boiled for some time in strong nitric acid without 

 losing its shape. All the organic matter is thus removed, 



and the skeleton of the 

 stem remains in pure 

 silica a most beauti- 

 ful object when seen 

 under polarized light. 

 It not only shows the 



FIG. 130. A, a spore of Equisetum with 



the elaters closely wrapped about it ; B, general Structure OI 

 the same with elaters extended. (After t ^ e epidermis, but pre- 

 Carpenter.) r . 



serves the stomata with 



their guard cells. The small leaves are arranged in whorls, 

 and, in the branching species, the branches are in whorls. 



References for Reading. Goebel's " Classification of Plants," pp. 

 256-273 ; Parker's " Elementary Biology," pp. 366-368 ; Vines' " Text- 

 Book of Botany," pp. 416-420; Bennett and Murray's " Cryptogamic 

 Botany," pp. 100-113, 124-130 ; Bower's " Practical Botany," pp. 325- 

 340. 



CLASS III. The Club Mosses (Lycopodince). These 

 are principally perennial plants with creeping stems. 

 Some are homosporous, others are heterosporous. Some 

 of them resemble in the character of their leaves different 

 species of Conifers so closely that they have the common 

 names of Ground Pine, Running Pine, Ground Cedar, 

 and Ground Fir. The resemblance is still further car- 

 ried out in the conelike spikes that some species bear on 

 upright branches. These spikes are made up of scalelike 

 leaves, each bearing on the inner side near the base a 

 somewhat kidney-shaped spore case which, when ripe, 

 opens transversely near the upper part and discharges 

 quantities of fine sulphur-colored spores, all of one kind. 

 The first stage of the development of the Club Mosses 

 from the spores is little understood, as the prothallia have 

 been seen and studied in only a few species. The spores 

 contain a large amount of oil, so that they are very in- 



