22 



The Naturalist, 



persistent, so that tlie Juration of the two generations is more nearly 

 equal. 



The order of the horsetails, Equisetaceae, now contains but a single 

 genus, Equisetum, not large, but of nearly world-wide distribution ; 

 the order is also of high antiquity, and of great importance to the 

 geologist, since it includes the gigantic and well-known plants of the 

 coal measures, Sigillaria, Calamites, &c. The horsetails have erect, 

 hollow-jointed stems, bearing toothed sheaths, and whorls of branches. 

 The fructification consists of capsules borne on the under surface of 

 umbrella-shaped scales, which are clustered together into a cone at 

 the end of the stems. The spores bear four long elastic arms, which 

 are coiled tightly around them when moist, and unroll when dry : so 

 that the spores when breathed on under the microscope, twist and 

 writhe about in the most striking manner. The germination is 

 similar to that of ferns. 



The Marsiliacese contain but a single British species, the pilTwort, 

 a small creeping plant with grass-like leaves, but spirally coiled 

 when young, like those of ferns. The fruit consists of brown capsules 

 like peppercorns ; these are divided by partitions into four cells, each 

 cell containing many membranous sacs. The sacs at the upper part 

 of the cells contain many small spores, those at the bottom of the cell 

 but a single large spore. The small spores contain moving filaments 

 like those in the antheridia of ferns and mosses ; the large spores 

 have a hole in the outer coat through which a portion of the inner 

 coat protrudes and becomes developed into a prothallus, bearing 

 archegonia, which are fertilized by the contents of the small 

 spores. 



The Lycopodiace^, or club-mosses," like the horsetails, are a small 

 order, but found in all parts of the world, and are of great antiquity, as 

 the huge Lepidodendron of the coal measures belonged to this order. 

 Some are rigid and leafy, like miniature conifers ; others are more 

 like mosses in habit, but may be readily distinguished by the leaves 

 containing bundles of spiral vessels. The greenhouse plants which 

 gardeners call mosses, are really club mosses— Se laginella. The 

 fructification is entirely different from that of mosses, the spore cases 

 are sessile in the axils of the leaves, and are of two kinds — one 

 kind containing small and the other large spores. The germination 

 is similar to that in the pillwort, In the genus Lycopodium only the 

 small spores are met with. 



(To be continiied.) 



