68 THE ESSEX NATURALIST
FORMATION OF COLONIES
So far as the Volvocales are concerned the details of colony
formation are well known. In the simpler cases (e.g. Eudorina)
all the cells of a colony, or coenobium as it is usually called in
this group, divide into a definite number, often thirty-two, of
daughter cells which keep together when liberated by the break-
ing up of the parent colony. In other cases only certain cells
in the posterior half of the colony divide.
Of the groups other than the Volvocales very little is known
about the formation of the colonies, but they probably originate
by the rapid division of single detached units, or of "swarmers"
liberated from a unit or from a "cyst" or spore. In the
Chrysomonadinae the whole colony may divide into two (e.g.
Synura, etc.) and this may perhaps also occur in the case of
Pelosphaera and the Zooflagellates. In Conochilus the unit
rotifers forming the colony increase in number by the develop-
ment of eggs deposited in the central jelly, but the actual origin
of the colony is unknown.
REFERENCES
Jane, F. W. 1947. The Colonial Habit in some Lower Organisms. Essex
Naturalist, vol. 25, Part I.
Koppe, F. 1924. Die Schlammflora des ostholsteinischen Seen und des
Bodensees. Archiv fur Hydrobiologie. Bd. xiv, pp. 619-72.
Lauterborni. R. 1906. Zur Kenntniss der sapropelischen Flora. Allgem.
Bot. Zeitschrift, pp. 196-7.
------------. 1916. Die sapropelische Lebewelt. Vehr. naturh.-med. Ver.
Heidelberg. Bd. 13, pp. 395-481.
ORTHODONTIUM GRACILE IN EPPING FOREST
BY JOSEPH ROSS
IN December 1946, Mr. J. H. G. Peterken showed to a small
party the moss Orthodontium gracile Schwaegrichen growing
in quantity on a log situated some distance to the east of
Ambresbury Banks, Epping Forest. When he first found the
moss at this station it was growing with Tetraphis pellucida
Hedwig, and since then O. gracile had extended at the expense
of T. pellucida. Mr. Peterken has had the moss under obser-
vation since 1942, and having seen it in mature fruit in summer,
he determined that the plants belonged to the variety hetero-
carpum Watson. This has been confirmed by Dr. Walter
Watson, who first found the variety in England and named it.
The typical form has a sub-erect, thin-walled, narrowly
clavate capsule with a slender tapering neck, whereas in the
variety the capsule is shorter, broader, often somewhat gibbous,