196 TRANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



of direct sunlight, it was noticed that at the same time 

 the rapidity of growth of the pollen tube was also checked. 

 To determine this retarding influence of direct sunlight 

 upon the growth of the pollen tubes more accurately 

 detailed comparative experiments were made. A culture 

 solution containing fresh Narcissus pollen was divided 

 into two equal portions, one of which was placed in a tube 

 covered externally by several layers of black asphalt 

 varnish and the other in a similar, but clean, glass tube. 

 On taking the temperature of these tubes when exposed 

 to sunlight it was found that the temperature of the tube 

 covered with asphalt was higher than that of the clean 

 glass tube but on pasting thin white paper on the more 

 absorptive black surface the temperature of the two tubes 

 became approximately equal. Thus in tubes half filled 

 with sugar solution : 



1. Asphalt tube exposed to sunlight, temperature was 

 21-5°C. 



2. Clean glass tube exposed to sunlight, temperature 

 was 20'5°C. 



3. Asphalt tube covered with white paper exposed to 

 sunlight, temperature was 20'6°C. 



4. Asphalt tube covered with white paper in shade, 

 temperature was 145°C. 



5. Clean glass tube in shade, temperature was 14*8°C. 

 In (3) when exposed to sunlight the temperature is only 



*1 higher than in (2) and in the shade or at night the 

 temperature in the darkened tube is *2 or '3 lower. 

 These differences of temperature are too slight to be able 

 to markedly affect the growth and elongation of the pollen 

 tubes. 



A much more difficult matter was to obtain sufficiently 

 long periods of exposure to sunlight. Time after time an 

 experiment started in bright sunlight was spoilt by the 



