154 
As the eggs of Dictyota dichotoma approach 
maturity, two layers can be distinguished in the 
walls of the oogonia, of which the inner becomes 
very thick as the egg ripens. In the discharge of 
the egg, the outer wall is burst, while the inner, 
still enclosing the egg, is protruded and is soon 
dissolved, freeing the egg and allowing it to round 
up. The outer layer of the oogonium wall then 
appears as a ruptured, crumpled membrane. 
The discharge of the tetraspores was not ob- 
served, but probably occurs by the same mechan- 
ism since the young, mature and empty walls of 
the tetraspore mother cells show the same appear- 
ances as those described for the eggs. 
Both at Naples and at Beaufort, North Caro- 
lina, the discharge of eggs in the laboratory began 
very early in the morning, when daylight was just 
visible or even, at times, before the slightest trace 
of light was discernible. At Beaufort, the time 
when this discharge commenced varied in different 
summers, and in the latter part of any one sum- 
mer, but was fairly constant for the earlier 
months of each summer. Both at Beaufort and at 
Naples, about 70-80 per cent. of the eggs liber- 
ated in any one day were discharged within the 
first half hour and about 80-90 per cent. were dis- 
charged within the first hour. At Beaufort about 
70-80 per cent. of the entire crop of eggs were 
thus liberated within a single hour of one day 
of each month. 
Attempts to alter the time of the discharge by 
subjecting the plant to various conditions of light 
and darkness were effective only as they affected 
the healthy condition of the plant. The attempt 
to induce liberation at other times of the day by 
exposure to various degrees of light, or to alter- 
nating darkness and light, was entirely without 
success. Discharge occurred as abundantly in 
dishes covered with red and with blue glass as in 
dishes covered with white glass. 
The tetraspores were liberated throughout the 
day, although the majority were discharged before 
7:00 am. Attempts to alter their rate of dis- 
charge by exposure to various conditions of light 
and darkness gave no marked result. 
The experiments indicate that the light rays 
affect the liberation of eggs and spores by their 
effect on the well-being of the plants, rather than 
by acting as a direct stimulus to the discharge of 
these cells. 
Alternation of Generations in certain Floridee: 
I. F. Lewis, Randolph-Macon College. 
SCIENCE 
[N.S. Vou. XXXV. No. 891 
Species of several genera of Floridew have been 
cultivated during the past two summers at Woods 
Hole. By using the method employed by Hoyt 
with Dictyota it has been found possible to rear 
to maturity sporelings of known origin. In this 
way it has been shown that in Griffithsia Borne- 
tiana and in Dasya elegans tetraspores without 
exception gave rise to sexual plants, which in 
Dasya were mostly male, and in Griffithsia about 
half male and half female. In Polysiphonia vio- 
lacea carpospores produced, also without excep- 
tion, tetrasporic plants. Hundreds of cases were 
observed. The experiments cited may be regarded 
as proof of the assumption, on cytological 
grounds, that there is an alternation of sexual and 
asexual individuals in Floridee producing both 
tetraspores and carpospores. 
The Germination of the Spore of Nemalion mutl- 
tifidum: I. F. Lewis, Randolph-Macon College. 
After being shed, and attaching themselves to 
some hard substratum, the spores of Nemalion 
remain without visible change save a slight in- 
crease in size for twelve to twenty-four hours. 
The center of the spore is occupied by the large 
chromatophore with its pyrenoid, the latter bear- 
ing a marked resemblance to a nucleus, but larger. 
The small nucleus lies to one side of the pyrenoid. 
The first sign of germination is the protrusion of 
a germ tube through the spore wall. Into this the 
pyrenoid passes, along with most of the proto- 
plasm. The spore cavity is left nearly empty. 
The nucleus, lying at the base of the germ tube, 
divides in the manner described by Wolfe for the 
nuclei of vegetative cells. One of the resulting 
daughter nuclei passes into the germ tube, the 
other into the spore cavity, where it becomes 
closely appressed to the wall as a structureless 
mass. The number of chromosomes in the first 
and later divisions is probably 8. A cross wall 
separates the germ tube from the nearly empty 
spore body, the latter taking no further part in 
development and soon dissolving in the sea water. 
The germ tube continues to elongate, and its 
nucleus divides in the usual way. The pyrenoid 
divides at about the same time, and a second cross 
wall cuts the germ tube into two parts, each with 
nucleus, chromatophore and cytoplasm. The apical 
cell so formed grows in length and divides. 
Repetition of this process results in the formation 
of a monosiphonous filament. 
Nuclear Division in Spirogyra setiformis: F. Mc- 
ALLISTER. 
