Studies in the Dictyotaceae. 
II. The Cytology of the Gametophyte Generation. 
BY 
J. LLOYD WILLIAMS, 
Assistant Lecturer in Botany , University College , Bangor . 
With Plates XII, XIII, and XIV. 
I N a previous paper the development, germination and cytology of the 
tetraspore in Dictyota and other members of the group were described. 
In the present paper it is proposed to deal with the development of the 
oosphere and antherozoid, the fertilization of the ovum and its subsequent 
segmentation, together with the parthenogenesis of unfertilized eggs — 
the observations in this case applying to Dictyota dichotoma only. 
In this plant the male and female gametes are borne upon different 
individuals. Excepting so far as the reproductive cells themselves are 
concerned, there is no difference either of form or of structure between the 
tetrasporic plants on the one hand and the sexual ones on the other. It is 
true that the latter generally have the branches of the thallus broader 
than those of the former, but to this rule there are frequent exceptions. 
As already described, the discovery of motile antherozoids, first made 
in 1896, was not confirmed till nearly a twelvemonth after. Subsequently 
the astonishing fact was established that, unlike the tetraspores, both the 
oogonia and antheridia are developed simultaneously in fortnightly crops, 
each crop being initiated a little before the lowest neap tide, and arriving 
at maturity about the period of the highest succeeding spring tide. The 
gametes thus produced are liberated during two or three days while the 
high tides are on the wane. A regular succession of crops continues thus 
from July to the end of October. So far as I am aware nothing like this 
remarkable periodicity has hitherto been observed in the case of any other 
Alga. During the last six summers careful records have been kept of the 
appearance of these crops, and their relation to the conditions of their 
environment. The data thus collected, together with a discussion of the 
factors concerned, will be published in a separate paper. These observa- 
tions only apply to the plant as growing on the North Wales coast ; it 
[Annals of Botany, Vol. XVIII. No. LXX, April, 1904.] 
O 
