114 WAYSIDE AND WOODLAND FERNS. 



Mud Horsetail (Eqnisetnm Kmoswn). 



The Mud or Smooth Horsetail is certainly the commonest 

 of the British species, for not only is it widely distributed, 

 but where it occurs it is in enormous colonies, sometimes 

 extending over acres of lakeside. Large ponds are sometimes 

 completely filled up by it, to the exclusion of almost all other 

 plants. 



Occasionally, the Mud Horsetail may be found with more 

 or less irregular whorls of branches, but the prevailing con- 

 dition of the stem is absolutely bare of branches from top 

 to bottom. Even where branches are present, it is usually 

 only to the extent of one or two each from a few of the upper 

 joints, as appear in our photograph, and they take an upward 

 direction. (Plates 122, 127.) 



The fertile and barren stems are alike save for the presence 

 of the cone on the former. The stems are slender, of various 

 lengths up to about four feet, perfectly smooth to the touch, 

 although finely scored with many shallow grooves, and of a 

 beautiful shade of green. The sheaths are short, and cling 

 closely to the stem, their teeth short, sharp, stiff, and with black 

 tips. The cones are short and egg-shaped or oblong ; they 

 are ripe in June and July, and are often borne at an angle with 

 the stem as shown in our plate. 



The stem in section shows a central hollow equal to two- 

 thirds of the diameter, and both inner and outer margins even. 

 The small breadth of tissue between them is perforated by 

 a series of ovals whose long axes are parallel with the outer 

 rim, and an inner series of small circular tubes. The ovals, 

 however, sometimes become circles, which occupy nearly all 

 the space between the inner and outer skins. 



A form with longer tapering branches, the upper part of the 



