S4 THE HORSETAILS. 



vegetative impulse seems to exist in different proportions 

 in each one, some having so httle that they do not sur- 

 vive the spring fruiting. It is interesting to know that 

 the size of the sheaths varies with the kind of stem, 

 being largest in the evanescent fertile stems, of medium 

 size in those fruiting stems that later bear branches, and 

 smallest in the wholly sterile ones. Before the fertile 

 stems have produced branches, they are much like the 

 fertile stems of the field horsetail, except that they are 

 usually shorter, slenderer, paler in colour, and with less 

 flaring sheaths. They have been described as sea green 

 with pale sheaths tipped with long, pointed, white- 

 margined brown teeth. The catkins are about cylin- 

 drical, an inch long, and a quarter as wide, and perish as 

 soon as the spores are shed. 



The sterile stems are erect, fifteen inches to two feet 

 in height and very slender. They are white or pale 

 green in colour and contain from eight to twenty grooves. 

 Below, the stems are smooth, but toward the apex the 

 ridges are thickly set with tooth-like projections of silex 

 which are frequently large enough to be seen with the 

 unaided eye. The sheaths closely encircle the stem, 

 and are pale green, tipped "with white-margined brown 

 teeth similar to those of the fertile stems. In the upper 

 two thirds of the frond, each node gives rise to a whorl 

 of simple, jointed, three or more -angled branches. 

 These are peculiar for having the joint nearest the stem 

 short and bent sharply downward, while the rest of the 

 branch is spreading or ascending. This character is one 

 that the eye readily appreciates. 



The shade horsetail is found in the North Temperate 

 and Arctic Zones of both hemispheres. According to A. 

 A. Eaton it ranges southward to New Jersey, Michigan, 



