56 BOTANICAL GAZETTE [ JANUARY 
After about two months, on the day when general liberation of the 
sexual cells occurred, when therefore all sexual plants could be certainly 
distinguished, these three shells were brought to the laboratory and 
examined. Each shell bore many plants of Dictyota 1.2-15°™ high.° 
Every plant was removed and examined under the microscope. The 
shell to which fertilized eggs had attached themselves bore 33 plants 2.5- 
15°™ high, all fruiting and all tetrasporic, as was shown by the presence 
of tetraspores or tetraspore mother cells on every plant. The two shells to 
which tetraspores had attached themselves bore 64 plants 2.2-13-75°™ 
high, all fruiting, and all sexual, and a few plants 1.2-2.5°™ high which 
were sterile. In handling these cultures many fragments were broken off; 
these were all examined with the microscope in order to be certain that no 
plant from any culture was overlooked. The evidence from these frag- 
ments agreed entirely with that given above for whole plants. 
Since these cultures were placed in the open harbor, the possibility of 
contamination by spores or eggs floating in the water must be considered. 
In fact, a few specimens of several other species of algae and many animals 
(ascidians, worms, molluscs, hydroids, etc.) did attach themselves to the 
shells. However, the fact that all the 33 plants on the shell to which 
fertilized eggs had attached themselves were tetrasporic, and all the 64 
fruiting plants on the shells to which tetraspores had attached themselves 
were sexual, seems convincing evidence that no contamination by Dictyota 
spores or eggs occurred. Thus the belief in the alternation of tetrasporic 
and sexual generations in Dictyota dichotoma, previously based on cytological 
evidence alone, seems proven by the results of these cultures. . 
As was noted above, each of the cultures of sexual plants was produced 
from the tetraspores of a single plant. One of these cultures bore 17 plants 
(4 females and 3 males), the other bore 47 plants (26 females and 21 
males). The tetraspores of a single plant are thus seen to produce plants 
of both sexes. From the proportion of male and female in the latter 
- culture and from the fact that plants gathered in the harbor at random 
show males and females in nearly equal numbers, the possibility is suggested 
that half of the tetraspores produce males and the other half produce 
females. Material has been preserved for a cytological study of this plant, 
to discover whether sex determinants occur in this species. These an 
other results bearing on the process of reproduction in Dictyota will be 
given in a subsequent article. 
This work has been done at the laboratory of the Bureau of Fisheries 
6 This rate of growth is much less than that observed in Dictyota under other 
conditions, 
