EQUISETACEJE. 153 



Rootstock rather slender, solid, with oblong pubescent tuber-like 

 excrescences. Sterile stems erect, decumbent, or prostrate ; when erect 

 it is usually 1 to 2 feet high or even more, and frequently terminates in 

 a long portion bare of branches, and is about the thickness of a crow- 

 quill in the lower part, which commences to branch at the extremity 

 of the 5th to the 14th internode, but usually about the 8th from the 

 base. The colour is rather dull green, and the general form some- 

 what pyramidal or cylindrical, tapering from about the middle 

 upwards. When growing in cultivated land a great number of 

 decumbent or prostrate stems are produced, with long branches 

 generally few in each whorl. In the form named alpestre, by 

 Wahlenberg, which grows at Micklefell, Teesdale, the sterile stem is 

 short, 2 to 3 inches, prostrate, with an ascending terminal point and 

 subsecund branches. I have seen a similar form on the shores of 

 Loch Leven. 



The fertile stem is 4 inches to 1 foot high, with 4 to 8 sheaths. 

 The spike is § to 1^ inches long. 



The fertile form, which afterwards throws out branches, appears to 

 be much rarer in E. arvense than in E. maximum. I collected in 

 September, 1838, by the side of Gartmorn Dam, near Alloa, Clack- 

 mannanshire, a fertile form, with a few branches at the base, which 

 resembles the form called E. riparium by Fries, but its sterile stems 

 are more branched. In 1874 a good many late fertile stems came 

 up at Balmuto in the month of June ; at first they were quite 

 unbranched, but distinguishable by their green colour and faintly 

 ribbed surface ; their sheaths were green, less deeply sulcate than 

 those of the ordinary fertile form. Most of these I gathered and 

 dried as specimens. I do not know whether they would all have 

 produced branches or not, but in July I found in the same place 

 several specimens with developed branches, sometimes in complete 

 whorls, but generally only 2 or 3 ; since that year only the ordinary 

 forms of fertile and barren fronds have appeared. This form, when 

 fully developed, is the var. campestre of C. F. Schultz, and the var. 

 serotinum of F. W. Meyer ; but I believe it to be only an accidental 

 variation, not a variety. 



Com Horsetail. 



Section II.— SUBVEKNALIA. A. Braun. 



Stems of two kinds. Sterile stems appearing at the same time as 

 the fertile stems, or shortly after them, and perishing in winter, 

 green or whitish, branched. Stomata level with the surface. Sheaths 

 with persistent teeth. Branches in regular whorls, without any 

 central cavity. Fertile stems appearing in spring, and remaining 

 until autumn ; at first somewhat succulent, whitish or fawn-coloured, 



VOL. XII. x 



