1910] : BRIEFER ARTICLES 55 
showing differentiation into wall cells and a central mass of cells like sporogenous 
tissue. 485. 
1G. 9.—The walls of the cells of the central mass are becoming mucilaginous 
and some of the nuclei are disintegrating. 485. 
Fic. 1o.—The mucilage cavity is formed, some nuclei still floating in the 
fluid contents, others being flattened against the wall. 485. 
Fic. r1.—Section of an early stage of a mucilage duct in a leaf, showing cells 
resembling sporogenous tissue. X< 485. 
ALTERNATION OF GENERATIONS AND SEXUALITY IN 
DICTYOTA DICHOTOMA 
After the failure of many attempts made during the past three summers 
to raise Dictyota dichotoma (Huds.) Lamour. from the spores and fertilized 
eggs to maturity, I have succeeded in raising nearly 100 plants to a fruiting 
condition. Since all attempts to raise plants to maturity in the laboratory 
have failed so far, the cultures were started in the laboratory and then 
transferred to the harbor. The method employed was as follows. Several 
days before the time for the maturing of the crop of sexual cells, when 
therefore no eggs were present in the water to serve as a possible source of 
contamination, two good fruiting tetrasporic plants were gathered late in 
the afternoon and placed in two jars of sea water, one in each jar. Since 
the spores will not attach themselves to glass, oyster shells which had lain 
on land for several years were placed in these jars. On the following day 
many tetraspores had been liberated and had attached themselves to the 
shells. The parent tetrasporic plants were then removed. | 
On the day when eggs and spermatozoids were mature, several sexual 
plants were gathered late in the afternoon and placed in a jar of sea water 
with oyster shells in the bottom, as before. Abundant liberation of eggs 
and spermatozoids occurred the next morning, as usual, and the parent 
sexual plants were then removed. 
Three cultures were thus obtained, one containing fertilized eggs, and 
the other two containing tetraspores, each of the latter containing the 
spores from a single plant. These cultures were placed in front of a 
north window of the laboratory. 
After about two weeks, when the young plants had reached a height of 
I.5-2™™\5 one shell bearing many young plants was removed from each 
of these jars and suspended between posts about 30°" below low water in 
a favorable situation in the harbor, and all plants of Dictyota in the imme- 
diate vicinity were removed. 
5 This rate of growth is probably less than normal, since — of Dictyota grow 
much more slowly in cultures than they do under natural conditi 
