—82— 



in patches in hard gravel with a small terminal spike (vulgare). 

 Outlying plants of this will be prostrate or ascending like 

 arvense decumbe7is {arvensiformis), and where there is little 

 competition and sufficient moisture, in recently disturbed sand it 

 bears a few twiggy branches at a decumbent base, while the long 

 erect portion is naked {humile ?). Finally at the very uppermost 

 river border, in gravel with a little humus, shaded by overhang- 

 ing trees or bushes, it is tall, erect, branched from near the base 

 to near the summit, the branches regularly decreasing from the 

 middle each way, the most beautiful form of the species and 

 next to sylvaticum the finest Equisetum we have. 



Now it is arve7ise in appearance, now fluviatile, now p al 'us - 

 tre; but widely as the extremes differ in appearance a most 

 abundant supply of intergrades is usually at hand, showing con- 

 clusivelv they are the result of environment alone. 



It can be distinguished from arve?ise with a lens, as the 

 angles of the branches are less prominently winged and the 

 siliceous coat is disposed in cross- bands, while in the other 

 species it is in punctiform dots. In section the stem is different 

 from arvense in wanting the yellowish line separating the two 

 cylinders, and in having one about the carinal canal, which 

 arvense ofteier want. From any form of fluviatile with which 

 it is liable to be confounded it may be distinguished by its more 

 open sheaths, broader margined cohering te th and narrower 

 central and vallecular canals The branches are thicker walled or 

 solid, more winged, usually 3 or 4 angled, whilein those of fluvia- 

 tile the walls are thinner, the angles lower, mostly five or more. 

 The ribs of the dried plants are flat and often appear as if 

 grooved because of the transparency of the bast. The sheaths 

 are also looser, through shrinkage of the stem. I find that by 

 breaking the stems of fresh plants just beneath the node, 

 those of fluviatile show a somewhat star-like central opening, 

 while those of litorale are larger and round. This is the easiest 

 test I have yet found. 



The section illustrated in Britton & Brown (Fig. 81) is 

 doubtless of fluviatile, as it has no vallecular cavities, which are 

 always represented in litorale, at least in the American plant, 

 but are absent in fluviatile except in large stems or basal sec- 

 tions. Milde says that the vallecular cavities fail, but he figures 

 them, and my European specimens possess them. 



