The Causes of the Zoning of Brown Seaweeds. 61 
higher and higher on the shore; the order being the same as that 
of the zoning observed. It is noteworthy that Ascophyllum nodosum 
is the only species in which exposure to the air appears essential to 
the expulsion of gametes; in all the Fuci considerable dehiscence 
takes place even when they are not exposed, though the maximum 
efficiency may not have been reached. The experimental methods 
are, however, not sufficiently trustworthy to do more than to indicate 
the probabilities for the intermediate species, and to contrast the 
behaviour of the two extreme species. It will be remembered that 
the receptacles of Fucus serratus are only very slightly swollen, 
while those of Fucus spiralis and the other two species are enlarged 
and filled with mucilage, so that for Fucus serratus a short time of 
exposure would be as effective in drying as a much longer exposure 
for the other species. 
III.— Observations Connected with the Method of Expulsion 
of the Bundles of Gametes. 
Farmer and Williams (Phil. Trans. B. (1898), 190, p. 629-631), 
Oltmanns (Beitrage zur Kenntniss der Fucaceen. Bibl. Botanica 
3, 14, 1-19), Thuret (Ann. d. Sc. Nat., Bot. IV., 2,197-214), and others 
have shown that the bundles of gametes are extruded by means of 
the mucilage which collects in drops at the openings of the 
conceptacles, when they are exposed to the air. It should be 
noticed that this effect appears to be much more marked when the 
receptacles are exposed to a very moist atmosphere, than when 
they are left lying in the sunshine and wind, as was the case in the 
present experiments. On the shore, as Peierce has pointed out 
(Torreya, Vol. 2, No. 9, p. 134-136) the plants tend to lie over one 
another and so keep the air round the receptacles fairly humid ; 
this makes it difficult to imitate the real conditions of the shore. 
Farmer (loc. cit.) has also suggested that the long paraphyses 
occurring in the conceptacles play a part in the dehiscence 
mechanism. A chance observation led to the suspicion that this 
effect had, if anything, been underrated. A section was cut through 
the ostiole of a very ripe $ conceptacle of Ascophyllum nodosum 
which had been exposed overnight. After covering the section 
with sea-water and a glass, the ejection of about 20 bundles of 
spermatozoids through the ostiole was observed during a period of 
about half-an-hour. It was noticed that each bundle moved, from 
its point of attachment, between two of the paraphyses; also that 
its movement was by a series of irregular jumps, and further that 
