NOTES ON THE LIFE-HISTORY OF THE H YDRODICTYON. 63 
environment, as indicated above, but tbe asexual mode of repro- 
duction is more readily promoted than the sexual one. 
Period of reproduction. — Zoospores and gametes are formed at 
all seasons of the year, providing the surroundings are favourable. 
Early in the morning is, as a rule, the time when the motile bodies 
escape from the mother cells, but there is no inherent, fixed law on 
this point, as zoospores are developed in darkness in a solution of 
maltose, and in the light in a sugary solution. 
Commencement of the formation of zoospores. — The multiplication 
in the number of nuclei is the first indication of the formation of 
zoospores. Nevertheless, in cultures living in saline nutritive solu- 
tions this multiplication of nuclei takes place at the outset, and 
independent of the formation of zoospores, consequently when these 
are formed a new formation of nuclei is not necessary. Two or 
three times as many nuclei are usually present at first than can 
afterwards be detected, and this diminution in numbers is supposed 
to be due to fusion between themselves. At the commencement of 
the formation of zoospores the central portion of the protoplasm is 
broken up by numerous clefts, and finally becomes divided into 
numerous small polygons, separated by clear lines, and each con- 
taining a nucleus. The nucleus, at first central in each polygon, 
becomes peripheral, and forming a clear spot ; at this point the 
two vacuoles and the two cilia of the zoospore are differentiated. 
The liberation of the zoospores is effected by the swelling of the 
cell-membrane, which finally becomes ruptured and disappears. 
The zoospores, freed from pressure, swarm for about an hour, and 
being held together by fine protoplasmic threads, retain their 
original position relative to each other. Finally they come to 
rest, become clothed with a cell-wall, and form a symmetrical net. 
Formation of gametes or conjugating motile bodies. — The develop- 
ment of gametes agrees in the main with that of the asexual zoo- 
spores. The green layer of protoplasm contracts strongly, changes 
to a yellowish-brown colour, and forms a wide-meshed net, which 
eventually breaks up into polygons, as in the formation of zoo- 
spores, but the polygons are much smaller, and more completely 
separated from each other. The gametes are liberated by the 
rupture of the outer wall. During their escape they begin to 
swarm. The gametes are ovoid, contain a nucleus, two pulsating 
vacuoles, and two cilia. When free they conjugate in pairs. 
MUSCINEiE. 
The Anatomy and Physiology of Mosses. R. Coesfeld. ( Bot . Ztg., 
1892, 1 PI.) 
The following parts are present in the stem of Polytrichum com - 
mune. A central bundle of elongated cells, representing a rudi- 
mentary vascular-bundle-system ; the cell-walls of this portion 
alone give a pure cellulose reaction. A protecting sheath separates 
the central bundle from the cortical tissue. The cells of the cortical 
