426 Mr Eattray on the Distribution of 



while others from the same gathering, kept exposed to 

 the sunlight in a warm room, emitted their swarmspores 

 after five days, the average temperature of the room being 

 77° F. Had the specimens been exposed for longer 

 periods to such dissimilar conditions, other observations 

 have shown that the times of maturation would have 

 differed still more considerably. Specimens of Ectocarpus 

 siliculosus and E. littoralis, as well as 3Ionostromce, have 

 also been exposed in a similar manner, and in all cases 

 those at a higher temperature have been found to dis- 

 charge their swarmspores before those at a lower. In 

 shallow pools, too, the periodic elevations of temperature 

 of the water which occur during sunny days in summer, 

 between the periods of high tide, act directly in accelera- 

 ting the extravasation of swarmspores in many cases, and 

 thereby have a direct influence on the possibilities of 

 extension of the species. The unusually late period of 

 the year at which some species are capable of producing 

 swarmspores in certain seasons (e.g., Ectocarpus siliculosus, 

 &c., in December) is also due to the mildness of the 

 season ; and, on the other hand, the meagreness in size, 

 and in fruit-producing capacity, or the entire absence or 

 unusually late advent of some forms (e.g., Gloiosiphoniw, 

 Bangice, species of Callithamnion, &c.), can often only be 

 ascribed — just as in the case of phanerogams — to a greater 

 rigour of weather. 



It is, however, much more difficult to account for 

 certain spasmodic appearances which are now and again met 

 with in the case of some species (e.g., Gloiosiphonia capil- 

 laris, Bangice, &c.), when they occur in a given year in 

 great profusion, bear fruit, then disappear, apparently with- 

 out reason, for another period, to again occur some seasons 

 later in their original place. It is not enough to say 

 that the spores have been all swept away by the repeated 

 rush of water, since at other times they withstand these 

 movements without difficulty ; neither can it be alleged 

 that they are crowded out in their struggle with more 

 successful rivals, nor can the influx of chemical or other 

 ingredients into the sea at any point explain their tempo- 

 rary absence from any extended area, since the renewal of 

 water by the rapid ebb and flow of the tide renders the 



