the Marine Algce of the Firth of Forth. 429 



piece of planed wood in sea water, and leaving it exposed 

 to the iniluence of the water for some time before ex- 

 amining it. During the later part of August and the 

 earlier part of September 1884, I had several such pieces 

 of wood suspended in the water from the sides of the 

 floating laboratory, and after an interval of less than a 

 fortnight many diatoms had become fixed to them. At 

 this period, moreover, the specimens of Enteroraorpha 

 compressa, which occurred very abundantly between the 

 levels of about |- to ^ tide were rapidly discharging their 

 swarmspores. Porphyrcc (e.g., P. vulgaris) and Ectocarpi 

 (e.g., E. siliculosus and E. littoralis) were also abundant in 

 the ripe condition, but although specimens of the former 

 did not become attaclied to the wood, rapid growth of both 

 Enteromorphce and Ectocarpi were noted. The early stages, 

 especially of the Entcroraorpthce, which could not be well 

 observed on the pieces of wood, except by the general 

 green hue soon communicated to them, were recorded from 

 a series of experiments conducted in glass vessels in the 

 floating laboratory. Specimens of Enterornorpha com- 

 pressa approaching maturity were removed from their 

 position on the shore along with the pieces of the shale 

 upon which they grew. These were placed in cylindrical 

 vessels of moderate size, and left for a few days in the 

 same water, under the influence of a self-acting aerat- 

 ing apparatus. Small fragments of the specimens were 

 detached and examined at intervals under the microscope. 

 The progressive stages in the segregation of the proto- 

 plasm into zoospores, and their emission from the spore 

 mother cells, were frequently observed. 



More prolonged observations on the further development 

 of the spores — conjugation was not seen — were carried out 

 by placing slides with cells in the vessels containing the 

 ripe parent plants, and allowing them to remain in close 

 contact with the algse for a few days. The impact of even 

 the feeble currents, generated by the aerating apparatus 

 against the ripe thalli, were sufficient to bring about a 

 somewhat more active extravasation of the swarmspores, 

 and this was several times still further accelerated by 

 agitating the adult thalli somewhat more violently in the 

 water. Of the very abundant swarmspores emitted many 



TRAXS. BOT. SOC. VOL. XVI. 2 F 



