420 E. J. ALLEN. 



(m-q) showing little or none. At the end of three weeks the result was 

 quite different, for whilst the early flasks show^ed only moderate growths 

 and were already beginning to go off, a sure sign of contamination, two 

 amongst the later ones (m and o) showed very fine growths of a rich 

 brown colour and forming very long chains. The culture in flask o was 

 one of the best and most vigorous that I have obtained during the whole 

 course of my experiments, and sub-cultures from it remained excellent 

 for many months. 



The following table shows for the last few flasks of the series the times 

 that the Thalassiosira remained in the electrolysed water, and the kind of 

 growth that was obtained : — 



Plask. Time during which 



Thalassiosira. was in Result culture, 



electrolysed water. 



I. 2 min. 28 sees. Moderate culture, not persisting very long. 



m. 2 min. 43 sees. Very good culture, with long chains, second 



best of series. 



n. 3 min. sees. No growth of Thalassiosira. 



o. 3 min. 22 sees. Very fine culture, best of series, dark brown 



colour and very long chains. Remained 

 good for a long time and gave a long series 

 of good sub-cultures. 



f. 3 min. 40 sees. No growth of Thalassiosira. 



q. 4 min. sees. No growth of Thalassiosira. 



(Flasks a-k all gave moderate growths which did not persist, with the 

 exception of flask h (1 min. 44 sees.), which had no growth.) 



Peptone-agar plates inoculated with 1 c.c. from flask o showed bacteria 

 of two kinds only, a few large yellow colonies, and many minute, slow- 

 growing colonies. They were of quite a different character from plates 

 made from ordinary cultures of Thalassiosira, which were always crowded 

 with yellow colonies, mixed with a large number of large milk-white 

 colonies which liquefied the agar, both kinds of colonies developing very 

 rapidly. 



After some experience it becomes easy to distinguish a clean culture 

 of T. gravida from one which is much contaminated by bacteria, by the 

 character and progress of the growth. In a clean culture, at any rate 

 during the summer months when the light conditions are favourable, the 

 growth is much more rapid and vigorous, the tendency to form long 



