EQUISETACE^E. (HORSETAIL FAMILY.) 585 



SERIES II. 



CKYPTOGAMOUS OR FLOWEKLESS PLANTS. 



VEGETABLES destitute of proper flowers (stamens and 

 pistils), and producing, in place of seeds, minute bodies of 

 homogeneous structure (called spores), in which there is 

 no embryo, or plantlet anterior to germination. 



CLASS III. ACROGENS.- 



Cryptogamous plants with a distinct axis (stem and 

 branches), growing from the apex only, containing woody 

 fibre and vessels (especially ducts), and usually with dis- 

 tinct foliage. 



ORDER 135. EQUISETACE^E. (HORSETAIL FAMILY.) 



Leafless plants, ivith rush-like holloiv and jointed stems, arising from run- 

 ning rootstocks, terminated by the fructification in the form of a cone or 

 spike, which is composed of shield-shaped stalked scales bearing the spare- 

 cases underneath. Comprises solely the genus 



1. EQUISiSTUM, L. HORSETAIL. SCOURING RUSH. (Tab. 14.) 



Spore-cases (sporangia, thecte) 6 or 7, adhering to the under side of the angled 

 shield-shaped scales of the spike, 1 -celled, opening down the inner side and dis- 

 charging the numerous loose spores. To the base of each spore are attached 4 

 thread-like and club-shaped clastic, filaments (elaters), which roll up closely 

 around them when moist, and uncoil when dry. Stems striate-grooved, rigid, 

 the hard cuticle abounding in silex, hollow, and also with an outer circle of 

 smaller air-cavities corresponding with the grooves ; the joints closed and solid, 

 each bearing instead of leaves a sheath, which surrounds the base of the inter- 

 node above, and is split into teeth corresponding in number and position with 

 the principal ridges of the stem : the stomata always occupying the principal 

 grooves. Branches, when present, in whorls from the base of the sheath, like 

 the stem, but without the central air-cavity. (The ancient name, from equus, 

 horse, and seta, bristle.) 



