THE FERN BULLETIN 



VOL. VII. OCTOBER, 1899. No. 4. 



THE GENUS EQUISETUM WITH REFERENCE TO THE 

 NORTH AMERICAN SPECIES. 



By Alvah A. Eaton 



FOURTH PAPER. 

 Varieties of Equisetum arvense L. 



1. Irriguum Milde. Scape ascending or erect, 3-12 in. tall, 

 brownish above, pale green below, 10-12 angled, with usually 

 dependent spike. Branches verticillate below, or often for two- 

 thirds the length of the scape, simple or branched, sterile, or 

 bearing small, often proliferous spikelets. Stem with stomata 

 and chlorophyl. This in early spring is like the ordinary fertile 

 form, but close inspection shows that it is green on the joints 

 below, and at time of fruiting small buds are protruding in the 

 grooves. These develop into branches as the fruit spike decays, 

 withers and recurves. As the season advances the branches 

 usually bear branchlets, the dead portion above becomes de- 

 tached, and the rest persists, appearing like any ordinary sterile 

 stem. This form is analogous to the fertile stem of E. silvaticum, 

 at first without stomata or chlorophyl, but later developing them, 

 but it is never found as a distinct race. It is, however, common 

 in some localities, especially where the plant is extra vigorous, 

 usually in a moist, sandy place, or even in shallow water, where 

 Milde first discovered it. The spikes are at the best about May 

 15th, though its branches are not developed till June 1st, when 

 the spike is dried up. It differs from the variety campestre in 

 being at first normal, while the latter develops spike and branches 

 together. 



2. IVtmorosum A. Br. Stem erect, 1-3 ft. high, pale green, 

 nearly white or pinkish, 12-16 angled, naked below for one-third 

 its height, and smooth. Branches horizontal or slightly ascend- 

 ing, 5-8 inches long, 3-4 angled, with an occasional secondary 

 branch. This is the well-developed form, found usually in open 

 woods, in moist, rich earth, or by fences, under bushes, but occa- 

 sionally in meadows by water courses. Milde says the branches 



