348 'J'HE BOTANICAL MAGAZINE. ivoi. xxx. No. 359. 



they do not attune, as has been studied by Frank^^ in Chlamy- 

 domonas tingens, to the strong intensity of light. In fact an 

 experiment with " Tuscheprisma " of Oltmanns', e.g. the ex- 

 periment in which the ray of light can reach the organism only 

 through a special light screen of prism containing agar-agar 

 with particles of Indian ink in suspension, showed that the 

 swarmspores formed a collection mainly in the region of the 

 moderate intensity' of light and neither of the strongest nor of 

 the weakest. Quite in accordance with this experiment the fol- 

 lowing experiment was carried on. A small rectangular glass 

 vessel with swarmspores was covered with a glass jar; the latter 

 being again covered with paraffin paper for avoiding the strong 

 intensit\' of light. In the next morning it was found that they 

 exhibited a positive phototaxis in the frontal one third region 

 of the base of the vessel. On removing the glass jar and par- 

 affin paper, they began immediately to move toward the side 

 of the vessel awa^^ from the w^indow, and after a lapse of time 

 it became clear to show a negative phototaxis. The intensity 

 of light w^as measured with a photometre " Infarible " to be 

 9:5"^ in either case covered or uncovered, that is to say, the one 

 being approximately double the other. The phototactic activity 

 of Chlatnydoinonas was recorded by Famintzin"'^ as early as 

 1867. 



I am not here in position to tell, whether the orienting 

 stimulations are dependent upon the distribution of the inten- 

 sitj^ of light, or upon the direction of the ray. 



In regard to the phototaxis I made another experiment to 

 get some idea about the relation between the sense of reaction 

 (positive or negative) and the condition of environment. Stkas- 

 BURGER''^ was perhaps the first to have carried out the study 

 on this point. It has been followed by many investigators. 



1) Bot. Ztg. Bd. 62. 1904. 



2) These figures show nuQiber uf .seconds, within wliich the bromide paper 

 changes its colour to that of the standard, so that tlie greater the number, the weaker 

 the intensity, and vice versa. 



3) Jahrb. f. wi.ss. Bot. Bd. B. 1867. 



4) Jena. Zeitsohr. N.F. Bd. 12. 1876. 



