336 BOTANICAL GAZETTE [NOVEMBER 
soon after sunrise. OLTMANNS (12, p. 523) speaks of a periodicity 
in the discharge of the gametes of the constantly submersed Fucacee 
(Halidrys, Cystoseira, etc.) as well as in Fucus. Fucus does not 
occur in the Bay of Naples, though abundant enough in most other 
parts of the ocean. It is ordinarily twice daily exposed at low tide, 
but as various authors’ have shown such uncovering is not necessary 
to the discharge of the gametes. The mechanism of the discharge 
of the gametes consists, in part, in the swelling of the gelatinous 
material in the conceptacles and the compression of the walls of the 
conceptacles by the surrounding tissues when the sexual elements 
are ripe. OLTMANNs expresses doubt whether these two factors alone 
furnish an adequate explanation of the process. As the matter now 
stands, these mechanical means do not account for the periodicity, 
unless we assume the relation of light to the processes connected wit 
the growth of the gametes and with the formation of gelatinous 
matters within the conceptacles. 
The periodicity coincides with the sequence of light after darkness 
and is as evident, as my experiments have shown, in forms having no 
conceptacles as in those that do have them. In Dictyopteris, the 
aplanospores (tetraspores) form on both surfaces of the flat thallus, 
near the midrib, and project more or less from the surfaces as they 
grow. Finally they escape through a slit in the wall of the mother- 
cell. They may even germinate (12, p. 486) before escaping: It is 
difficult to see where mechanical pressure can effectively er 
here except in the sporangium itself, that is, by the growth of 
spores and the gelatinization of the wall and residual contents (if any : 
of the spore mother-cell. I shall subsequently show that light favors 
the germination of the spores and the growth of the young plants 
though they will germinate and grow in darkness. It is poor 
therefore, that light favors the growth of the spores before they esr 
from the sporangium as well as after. In this we eee spores 
explanation of the connection of the periodic discharge of pee , 
in Dictyopteris and of the gametes in Fucus and Cystoseit ae 
mechanical means of discharge above discussed. The develo & 
light is favorable to the growth of the spores, therefore totheT™ 
ght 1s tlavorabie to the gro pores, 
ment of mechanical pressure by them, but as th 
ae 
; of a 
Sas 
e rapid dischne ae 
5 Cited by OLTMANNS, I. c. 
