224 



HARD WICKE 'S S CIENCE - G OS SI P. 



amount of moisture with which the spores are sur- 

 rounded there can be no doubt. Most probably it 

 takes place by the contraction and expansion of the 

 cells of which the elaters are composed, under the 

 varying influence of the moisture contained in the air. 

 The phenomenon is a very curious one, and should 

 by all means be seen by every one who possesses a 

 microscope. 



Fig. 188. Sporangium of Equisetum 

 arvense. 



Fig. 189. Transverse section of Fruit- 

 spike of ditto (twice nat. size), 

 snowing how sporangia are attached 

 to the axis. 



Fig. 190. Fruit 

 spike of ditto, 

 twice nat. size. 



Fig iqi. Fragment of the branched 

 stem of Equisetum fialustre. 



Doubtless the spores are endowed with this suscep- 

 tibility to hygrometric changes in order to ensure 

 their distribution, and thus the species is continued 

 in distant places. The spore on germination gives 

 origin to a cellular structure called a prothallus, upon 

 which the antheridia and archegonia are borne — 

 much as in Ferns. In former periods of the world's 

 history the Equisetacese occupied a much more pro- 

 minent situation in the vegetable kingdom than they 

 do at present. If we turn to the Palaeozoic strata we 

 shall find in the Carboniferous formation of that 



period abundant evidence of this. The reed-like 

 fossil Calamites most likely belonged to this order, 

 and the vegetation of the Carboniferous period is 

 made up of the genera Lepidodendron, Stigmaria, 

 Sigillaria, &c, belonging to the Lycopodiacea?, Equi- 

 setacere, and allied orders. 



This order also affords an instance of what has 

 been called homoplasmy, or likeness between plants 

 belonging to totally different orders, and even different 

 divisions of the vegetable kingdom. Thus the Equi- 



Fig. 192. Spore of 

 E. arvense, showing 

 elaters clasped round 

 (mag.). 



Fig. 193. Spore with 

 four elaters un- 

 coiled (mag.). 



Fig. 194. Fertile stem of Equisetum 

 arveuse, springing from rhi- 

 zome (natural size). 



setacerc of the acrogenous sub-kingdom has its coun- 

 terpart in the Hippurus, or Mare's - Tail, which 

 belongs to the division of flowering plants. 



It is often the case that botanical collectors give 

 a great deal of attention to the Ferns and Mosses, 

 and treat with comparative neglect the humble Cryp- 

 togams, including the Equisetacea;. This neglect 

 seems to be unmerited ; for, although the flowering 

 plants, doubtless, at first sight, form a more attractive 

 field for the display of the energies of the popular 

 botanist, yet any one who will take the trouble to 

 work at the Equisetacea; and allied orders, with lens 

 and microscope, will find, in the adaptation of means 



