II. The Cytology of the Garnet op hyte Generation . 189 
is completed a few days before liberation, the whole process occupying 
from six to ten days. Particular attention was paid to the later cell- 
divisions to see if any evidence of amitosis could be observed. As 
far as can be seen, however, all the usual stages of karyokinesis are 
repeated at each step, and after each cell-division the nucleus assumes the 
appearance of the resting condition. Several reliable countings of chromo- 
somes were obtained in the earlier mitoses, both in the prophase stage and 
in polar views of the equatorial plate stage (Fig. 11). All these agreed in 
giving the number as sixteen. Occasionally a larger number was indicated, 
but in all such cases it was easy to see that some of the bent chromosomes 
had their angles cut off, thus giving two chromatic segments instead of one. 
The first division-wall of the antheridium mother-cell is vertical to the 
thallus and at right angles to the long axis of the branch, the second 
is also vertical but parallel to the axis, so that in surface view four 
cells are seen. The succeeding divisions are not so regular, but a number 
of tangential division-walls appear before any further vertical ones are 
formed. Ultimately the antheridium in surface view is seen to consist 
of sixty-four cells arranged in four groups of sixteen. In vertical section 
there is great divergence between different antheridia, the number of tiers 
in some cases being twenty-four (Fig. 14), in others about twenty. The 
number of successive nuclear divisions must be about twelve, but it is clear 
that many of the cells fail to divide and others abort. It is instructive 
to note in this connexion that in many cases when the circumstances 
are unfavourable it is the lowermost cells in an antheridium that are 
first retarded ; this fact will be referred to again when discussing the 
importance of light as a factor in the development of the gametangia. 
Careful countings of the antherozoid mother-cells in a large number of 
antheridia show that the average number of sperms produced in an antheri- 
dium is about 1,500. It has already been shown that the number of 
oogonia in a sorus ranges from about twenty-five to fifty, while the number 
of antheridia is generally from 100 to 300. Taking the lower number 
in each case we see that for every egg in an oogonial sorus there will 
be 6,000 antherozoids in a sorus of antheridia. In order to form an 
approximate idea of the number of gametes produced by a single plant 
the sori were counted on a specimen twelve inches long. They were found 
to be over 3,500 in number. Allowing an average of 1,500 antherozoids 
for every antheridium this would give us a total of over 500 millions for the 
whole plant, a number which is certainly much too low for a vigorous, 
full-grown plant. If we consider a single locality, the Menai Straits for 
instance, where Dictyota flourishes in great abundance, and the vast 
multitude of sexual plants which on certain days every fortnight throughout 
the summer months fill the water in their vicinity with untold myriads 
of swarming gametes, we cannot but be filled with astonishment at the 
