112 



VASCULAR CRYPTOGAMS 



granular cuticularised exospore, and an inner endospore, composed of 

 unchanged cellulose. So strong is the hygroscopic property of the 

 elaters, that, even if lightly breathed on, the spores of Equisetum are 

 seen under the microscope to be in active motion, from constant changes 

 in the humidity of the air. The spores contain chlorophyll, and, in 

 consequence, retain their vitality only for a very few days, and germinate 

 in a few hours after being placed in favourable conditions. In this 

 respect they show a striking contrast to those of ferns. 



Fig. 84. —Stages in the development of spore of E. 

 litnosum ( x 800). i and e, outer coat from which the 

 elaters are formed : 2, 3, inner coats. (After Goebel.) 



Fig. 85. — Spor« with elaters extended (magnified). 



Fig. 86.—^. limnsum L. 

 Rhizome and tubers. 



The only mode of vegetative propagation known in the Equisetacese 

 is by the production of tubers on the rhizomes and on the underground 

 portions of the erect stems ; they are peculiarly modified internodes, filled 

 with starch and other food-materials, and may remain dormant for years. 

 The buds, especially those produced at the lower nodes of the erect 

 stem, also have the power of retaining their vitality for a considerable 

 pericd in a rudimentary condition ; and, when they vegetate, develop into 

 branches of great vigour. Tomaschek (' Oesterr. Bot. Zeitschr.,' 1881, 

 p. 245) induced prothallia of Equisetum to hibernate by growing them 



