112 THE BOG-MOSSES OF ESSEX.
The author, no doubt, had in mind the recent changes in the
classification of these organisms, which share with other large
and widely spread genera, such as Rubus, Rosa, and Hieracium
among land plants, and Potamogeton, the Batrachian Ranunculi and
the Harpidioid section of Hypnum among aquatics, that difficulty
of classification which arises from the presence of only very
slight differences and very great likenesses between the forms.
This characteristic aggravates the question as to what is a
species and causes great differences cf opinion among workers
in these groups.
In the following list the system of Warnstorf has been
followed.1 This system has been adopted by most Continental
and American writers, and in some of the more recent local
lists of Sphagna in this country.2 According to Warnstorf's
classification 41 species of Sphagna occur in this country, while
only 12 are recognised in the most recent book on British
mosses.3 This classification is based largely upon the position
of the chlorophyllose cells in the branch leaves and the
distribution of the pores in the hyaline cells, and is therefore
to some extent an artificial one, but the forms so distinguished
do, as a rule, according to my experience, correspond with what
appears to be a natural grouping of the plants themselves. (But
see note under Sphagna subsecunda below.)
Several lists have been published. I have been able to find
the following:—
(1) 1845. Greenwood, A. "Mosses found near Chelmsford."
Phytologist, Vol. ii.
(2) 1872. Parsons, Dr. A. F. "Mosses of London District."
Science Gossip, Vol. viii., p. 64.
(3) 1884. English, J. MS. list of Mosses of Epping Forest.
(4) 1890. Buxton, E. N. "Mosses." Epping Forest, Ed. III.,
pp. 135, 136.
(5) 1891. Marquand, E. D. "List of Mosses in Mr. E. G. Varenne's
Herbarium." Essex Naturalist, Vol. vi., pp. 33.
(6) 1900. Horrell, E. C. "European Sphagnaceae." Journal of
Botany, 1900.
(7) 1901 ? Dixon, H. N., MS. list of N. Essex mosses.
(8) 1903. Shenstone, J. C., Victoria History of Essex. Article
"Botany."
1 Horrell, E. C., "European Sphagnaceae," Journ. of Bot., 1900.
2 e.g., Ingham, W., "Sphagna of Yorkshire and Durham," Journ, of Bot., 1901,, p. 145,
3 Dixon, H. N. Student's Handbook of British Mosses. Ed. II. (1904).