534 Lloyd Williams . — Studies in the Dictyotaceae. 
some which were taken into the laboratory and kept in a damp 
chamber overnight and immersed in sea-water the following morning 
yielded motile antherozoids. On the seventeenth there was a general 
liberation of gametes in the Straits. In order to obtain abundance of 
swarming antherozoids it was not necessary on this occasion to place 
the male plants in a damp chamber overnight. By the evening of this 
day most of the female plants could be seen even with the naked eye 
to be clear of oogonia excepting for a few at the distal ends. By the 
eighteenth at least three-fourths of the crop had been cleared off : on 
the nineteenth only a few sori were left — most of these were the distal 
belated ones, others had been arrested just before maturity. On this 
day the first faint and undivided rudiments of the succeeding crop 
made their appearance. By the twentieth the whole plant was clear 
of the old crop, and the new antheridia, though still undivided, were 
more prominent in size and colour than before. 
In this particular case, general liberation took place about three 
tides after the highest spring. If in the diagram we connect this and 
the middle of the line of average development for each day, we get 
a curve which we may call the optimum of development. This we may 
safely regard as expressing the time of development of a single sorus, 
and the great majority of the sori in the locality coincide with it in 
their times of initiation and rate of development. 
In the case of this crop the diagram further shows that although 
some of the rudiments appear eight or nine tides before the lowest neap, 
and others as late as one tide after it, the majority are initiated about 
four tides before the lowest neap. The life of an average sorus from 
its first appearance to its discharge would be about nineteen tides (ten 
days) ; the width of the ‘ crop-band ’ is from eight to ten tides, and the 
whole time taken by the crop from the appearance of the earliest of 
the rudiments to the liberation of the latest is about twenty-eight tides. 
The presence of younger sori on the distal part of the reproductive area 
of certain plants has already been explained, and it is clear that such 
cases should be excluded from the diagrams, for in the case of plants 
which have ceased to elongate, and where the reproductive area reaches 
to the very apex, all the sori are practically in the same stage. It 
should be observed, however, that most of the distal sori thus belated 
in their initiation accelerate their development to such an extent that 
their liberation is not much behind the others, so that even including 
them the periodicity is still well marked. There are other circumstances 
which sometimes interfere with the periodicity — these will be dealt with 
further on — but they do no more than slightly modify the normal process. 
