o44 Proceedings of the Royal Physical Society. 
of molluscan fry from the warmer surface-waters of the 
Atlantic by way of the channel between Scandinavia and 
Shetland, and perhaps to even a greater extent by way of the 
Straits of Dover, which, as a channel of communication 
between the Atlantic and the North Sea, has only recently 
been established. There is thus a certain amount of com- 
petition going on between the shallower-water Mollusca of 
boreal and arctic origin, and the forms proper to the same 
conditions which are finding their way in from Celtic or 
Lusitanian provinces. It is only in the deeper parts of the 
Firth of Forth, which have not been affected seriously by 
the changed conditions, that we have any reasonable hope 
of meeting with the descendants of the primal stock of the 
Mollusca occurring at Leith. 
XXVI. On the Postponement of the Germination of the 
Seeds of Aquatic Plants. By H. B. Guppy, M.B,, 
Pearl Harbour, Oahu, Hawaiian Islands. 
(Read 17th March 1897.) 
The postponement of the germinating process in the case 
of aquatic plants displayed itself in the course of a large 
number of experiments conducted near London between 
1891 and 1896. That germination may be deferred to the 
third, fourth, and fifth years is sufficiently demonstrated in 
the appended Table of results; and from those experiments 
still in progress, it may be presumed that instances of a still 
greater delay will be in time afforded. This capacity is not 
necessarily connected with the hardness or with the imper- 
meability of the seed-coverings, as is well shown by the 
behaviour of Limnanthemum, although the stony fruits of 
Potamogeton and Sparganium exhibited it to a more marked 
extent. 
Unless otherwise indicated, the results given for aquatic 
plants in the Table were obtained from seeds and fruits never 
allowed to dry. A variety of other influences affected the 
experiments, such as those connected with the temperature, 
the amount of light, the employment either of water or of 
