EXPERIMENTAL CULTURES OF DIATOMS 



65 



Summary. 



The following plnnkton species may be recorded: as developing to a greater or less 

 extent in culture vessels of prepared sea wat^r : — 



Pleurosigma fasciola, Ohaetoceras diadema. 



Asterionella japonica, Ohaetoceras laciniosum. 



Tabellaria sp.? Ohaetoceras .contortum. 



Nitzschia closterium, Ohaetoceras decipiens. 



Nitzschia seriata, Ohaetoceras convolutum. 



Nitzschia hilohata, Biddulphia aurita, 



Thalassiothrix nitzschioides, oscinodiscus suhhulUens, 



Slceletonema costatum, oscinodiscus radiatus, 



Melosira hyperhorea, Nitzschia closterium. 

 Ohaetoceras dehile. 



Nitzschia closterium. 



As I previously stated Nitzschia closterium has been found capable of developing 

 in great luxuriance, and of replacing, under artificial conditions, a variety of forms. 

 Its optimum temperature is from 18° — 20° C. ; but it will endure a range of 0° — 23° 

 C. without loss of vitality. A preference for bright light is revealed by a comparison 

 between two cultures, which were grown for two months, the one opposite a bright 

 window and just out of the direct sunlight and the other in a northern sxposure. In the 

 former the frustules attained an average length of 59 fi, contained rich, 

 dark brown chromatophores, and were very active ; in the latter the average length was 

 35 fx, the form irregular, the chromatophores greenish and the move- 

 ment sluggish. These two cultures were grown in flasks lightly plugged with cotton, 

 but the best growth obtained was an uncovered beaker culture, developed later under 

 optimum conditions of light and heat. In this the frustules attained a length 

 of 112 [x and showed a tendency to form chain-like colonies. In one chain nine 

 frustules were counted and these moved over one another actively, with a motion 

 similar to that of Schizonema Grevillei. This would seem to indicate that the free 

 access to a considerable air surface is beneficial. In less favourable conditions the 

 frustules are frequently grouped in irregular masses of coleoderm. As regards size 

 and habit of growth it may be concluded that the environment may exert a very con- 

 siderable influence. 



Melosira hyperhorea, Grun. 



Cultures of Melosira hyperhorea. set up from material developed from the 

 plankton collection of July 4, were maintained from September 14, 1917, to March 22, 

 1918, and dealt with the following conditions: (1) air and light, (2) salinity, (3) tem- 

 perature. (4) develonment in artificial sea water. 



T. Air and Light. — Since it has been prev^"ously ascertained that Melosira requ'red 

 the addition of nutrient salts, all cultures were grown in sterilized treated sea water. 

 Cultures were set up on Sente^^ber 14, in open flasks and in others nlu'^ged with 

 cotton and placed: Cl) in north window, (2) in south window, (3) opposite south 

 window just beyond the d'rect rays of the sun. (4) in dark. The following table 

 briefly summarizes the results. — 



