the Marine Algce of the Firth of Forth. 435 



(1) the conditions of temperature, (2) the movements, and 

 (3) the purity, together with the movements of the water. 

 The first of these modifications was effected by allowing 

 embryos to germinate in a warm room, either exclusively 

 or intermittently ; the second, by artificially producing in 

 the glass vessel, with a strong glass rod, rapid and incon- 

 stant movements of the water; and the third, by adding 

 previously a considerable quantity of muddy material, in 

 order to increase friction during the movements. 



The effects of an elevation of the temperature of the water 

 by 10° F., the other conditions remaining constant were — 



1. An earlier discharge of swarmspores from the adult 

 plants by about one day, in the case of exposure to the 

 change, extending over a fortnight, for Enteromorpha com- 

 pressa and Ectocarpus siliculosus. (Compare pp. 425, 426.) 



2. An elevation of the temperature of the water on 

 alternate days only, in the case of other similar specimens, 

 delayed the emission of swarmspores. A healthy plant 

 in such circumstances emitted its swarmspores only four 

 hours before some others of the same species which were 

 in water whose temperature had never been elevated. 



3. In the case of specimens growing in the ordinary 

 water, the swarmspores were only observed in process of 

 extravasation during the day, the temperature being higher 

 than during the night. On several occasions specimens 

 were examined after nightfall, but no such process was 

 seen. 



Specimens of llonostroma lafissimum, Enteromorpha com- 

 pressa, E. intestinalis, and TJlothrix flacca were observed 

 in this connection, as well as ripe specimens of Ectocarpus 

 siliculosus and E. littoralis. 



4. The general effects on germination were as follows : — 



chiselled. Upon returning to the Carr in May 1814, in order to recommence 

 operations, it was matter of no slight surprise to find the surface again as com- 

 pletely invested with large sea-weeds as ever it was, although little more than 

 six months had elapsed since the work had been left off, when, as already 

 said, the rock had been cleared of weed. In particular, it was observed that 

 many newly-produced species of F. esculentus measured 6 feet in length, and 

 were already furnished with their fruit-bearing pinnte. The common tangle, 

 F. digitatus, was only about 2 feet long. It is to be observed that the speci- 

 mens here alluded to were taken from that part of the surface of the rock 

 which had been dressed off with the pick or chisel the preceding autumn ; they 

 had therefore grown from the seed." 



