Proceedings of Royal Society of Canada. 157 
Revision of the Canadian Equiseta.* 
By Gurorce Lawson, Ph.D., LL.D. 
“The genus Hquisetum, Tournefort, is composed of a com- 
paratively small number of existing species. They are 
plants with subterranean or submerged rhizomes, sending 
up hollow, jointed stems, which are either simple (un- 
branched) or bear verticils of branches at the joints, similar 
to the stems, but smaller in size. Both stem and branches 
are longitudinally grooved, and punctated with lines of 
stomata along the grooves. These plants are leafless, the 
foliar organs being reduced and cohering into tubular 
sheaths at the joints, with the leafpoints only free as teeth. 
The cuticle is more or less highly silicified, so that in some 
species the plant retains its form after its vegetable mat- 
ter has been removed. The genus constitutes a natural 
order by itself, well defined both by structural characters 
of the vegetable organization and peculiarities in the re- 
productive organs. Hven regarded as an order, these 
plants are isolated, cut off from near relationship with other 
groups. This fact, taken in connection with the differences 
of minute structure and modes of growth observable among 
the existing forms, and their wide geographical distribu- 
tion, indicates that they may be a remnant of what was 
formerly a more multitudinous group of species and 
varieties. Linnzeus (who is not the author of the genus, 
although always so credited) gave, in the Species Plantarum, 
seven species, of which only one (£. giganteum) was then 
(1764) known to exist in America. Alex. Braun, of 
Carlsruhe, prepared a Monograph of the North American 
species, which was translated from the author’s MS by the 
late Dr. George Engelmann, of St. Louis, and, with some 
additions, published in the American Journal of Science for 
October-December, 1843 (vol XLVI., No. 1, pp. 81-91). 
A synopsis of the Canadian species was published by the 
writer in the Edinburgh Botanical Society’s Transactions, 
in 1863 (vol. VII., pp. 558-564), and subsequent additions 
were made, in the Synopsis of Canadian Ferns and Filicoid 
Plants, in _ (Trans. Bot. Soc., Ed., VIII., pp. 20-50, 
2 
