EXPERIMENTAL CULTURES OF DIATOMS 



67 



It is seen at once that Metosira liyperhorea will endure a great diminution o£ 

 salts and can live for some time even in tap water in which salts are practically 

 lacking. The addition of Miquel nutrients, however, instead of acting favourably 

 proved fatal in- a short time. 



The above table has reference merely to the state of the chains examined micro- 

 scopically and not to the increase in size of the colony. With a reduction to lower 

 than 40 per cent little development occurred; but in from 40 to 100 per cent the 

 colonies were practically equal in size as well as uniform in quality. Increased con- 

 centration acted as a check to growth and caused disintegration in proportion to the 

 degree of concentration. The latter caused also much malformation due to thick- 

 ening of the walls, inward curving of the zone and irregular divisions. 



III. Temperature. — A healthy, normal colony was divided into sections as nearly 

 equal in size as possible a-ad each was placed in a separate flask, half filled with 

 treated sea water. The temperature of each was then slowly lowered or raised over 

 steam to the required degree. To pref\'ent contamination the thermometer was in 

 each case kept in a second flask, one of which had boon prepared for each of the 

 series. When the desired temperature was reached it was maintained for three 

 minutes and then allowed to return to normal. The series was set up on February 3, 

 a-nd gave the results tabulated below: — 



Temperature. 



March 3. 



.\rea of Surfaces. 



Condition. 



March 15. 



60°C.... 



50° .... 



46° ... 



40" ... 



35° ... 



30° .... 



26° ... 



20° ... 



15° .... 



10° .... 



5° .... 



0° .... 



5° ... 

 Frozen . 



Dead. 



27 sq. mm. 

 54 " 

 48 " 

 40 " 

 45 " 

 32 " 

 25 " , . 

 24 " 

 54 " 

 Scattered . . 

 15 sq. mm. 



Fair 



Excellent. 



Best of Series. 

 Poor 



Improved. 

 Excellent. 



Best of Series. 

 Disintegrated. 



It was noted in preliminary work that some frustules seemed capable of resisting 

 a temperature of 50° C, but it was evident from the development of the series that 

 their vitality was so impaired that subsequent growth was inhibited. That which 

 was raised to 40° revived and after six weeks presented a colony 90 per cent of the 

 frustules of which were in excellent condition. An increase or decrease of 20'° was 

 found to be no hi-adrance to development; but I regret that time did not permit of 

 ascertaining the length of time to which the organism might be submitted to the 

 changed, condition. One variation due to change of temperature, which was noted, 

 was the great ease with which the frustules could be separated. This indicates a 

 change in the mucilaginous substance by which the frustules are bound together. 



The flask lowered to -5°, which is recorded above as showing the best develop- 

 ment, was accidentally overturned and the contents scattered through the flask. It 

 was found that the chains in this were remarkably good, practically no disintegrated 

 frustules occurring. From this it may be inferred that in other flasks some disinte- 

 gration piay have been due to crowding. 



On March 3 many sporangial cells, similar to those found in the experiments on 

 light, were noted in all the flasks, even in the unheated controls. In the -5° flask some 

 had already divided. On March 15 all the cultures contained beautiful, long, broad 

 chains; and on March 22 they were still in the process of division. The broadest 

 chains noted had attained a diameter of 3'9ju., and in advanced cutures all 

 gradations were foimd down to a diameter of 10 /x. The sporangial form- 

 ation was (ilearly not due to the stimulus of temperature, since is was also noted in 

 the controls. In the latter, however, it was least pronounced, and it is probable 



79550— 5i 



