252 Mr John Eattray on the 



the plant was kept under daily observation. The clear 

 green and fresh colour of all the cells, however, at once 

 disproved all possibility of tliC presence of pjathological 

 conditions, nor is it unlikely that this number approximately 

 represents the average normal percentage for an ordinary 

 specimen of this alga. 



In the case of the fourth and fifth experiments the 

 specimens were also approaching the stage for extravasation 

 of the spores, inasmuch these were shed on the fifth day 

 after the experiments ceased ; while in the case of the first 

 plant, the results of which are recorded above, a similar 

 emission of motile spores only occurred after eight days. 

 Tlie general inference, therefore, that the maximuvfi of 

 oxygen evolution is reached at the time of sporulation seems 

 to he clearly ivarrantahle in this species, and the deduction 

 has been corroborated by some of the experiments recorded 

 on p. 251. 



The experiments in connection with this species, which 



is very abundantly represented in most localities of the 



estuary of the Forth, have been divided into two series, 



differing widely in the percentages of oxygen which they 



present. The first series was conducted during the month 



of September, and under very favourable conditions on the 



whole with regard to mildness and amount of sunshine. 



The latter, on the other hand, was undertaken in November, 



when the amount of sunshine was but small, and the night 



no longer mild. A comparison of the two series, therefore, 



shows that in the warmer autumn months there is a very 



pronounced excess of oxygen given out, as compared with 



what takes place at the approach of or during winter. It 



must also be noted, that although care was taken to procure 



sound specimens for all the experiments, greater difficulty 



was encountered in this respect in the latter series, and in 



one instance especially (Exp. XI.) the plant selected was 



somewhat injured along one of its margins. Owing to this 



difficulty, the second group of experiments were limited to 



five, but from a slight admission of air into the eudiometer 



tube during the process of analj'ses in two cases, the results 



so far obtained had to be abandoned. 



Among the plants chosen for the first group of experi- 

 ments, emission of spores was observed in none, yet all were 



