﻿i 5 i6] ADAMS— POLLEN GRAINS 133 



grains, and the drop was stirred with needles so as to make sure 

 that the surface of the pollen grains was wet and that they were 

 distributed uniformly through the solution. It was found in later 

 experiments that the pollen grains germinated much more rapidly 

 if a very thin layer of liquid was spread on the slide than if a large 

 hemispherical drop was used, the reason being presumably that 

 oxygen was more readily obtained by the pollen grains in the former 

 case. Cover glasses were not used, as they prevented germination 

 except along the edges. The prepared slides were then placed on 

 the surface of damp blotting paper in Petri dishes and the cover 

 replaced. In other cases a larger number of slides was placed on 

 blotting paper in a glass dish with flat bottom and a glass plate 

 was used as a cover. The presence of the damp blotting paper 

 served to dimmish evaporation of the sugar solution. 



On May 6, 1913, two sets of cultures were started at 4:00 p.m. 

 One was kept in the laboratory, the temperature of which at this 

 time was 14? 5 C, the other being placed on the window ledge out- 

 side, which faced toward the north, so that direct sunshine could 

 not reach it. The temperature outside at the time of starting the 

 culture was not observed. The cultures were examined daily 

 during the next 3 days. It was found impracticable to keep them 

 going longer than 3 days, owing to the occurrence of Penicillium. 

 The strengths of sugar solution, as stated above, were: (a) 5, (b) 10, 

 (c) 15, (d) 20, 0) 25, (/) 30, (g) 40, and (h) 50 per cent. The results 

 were as follows: 



A T . — Inside cultures: 1:00 p.m., May 7; temperature i3°C: 

 (a) nearly every pollen grain had germinated; some had quite 

 long tubes, while others had shorter tubes; (b) almost every pollen 

 grain had germinated and formed a very long tube; (c) many had 

 germinated and formed short tubes; (d) a considerable number had 

 germinated and formed short tubes; (e) and (/) same as (d); 

 (g) none had germinated; (h) none had germinated and very few 

 of the pollen grains had swelled. 



Bi.— Outside cultures: 1 :oo p.m., May 7; temperature 10? 5 C: 

 (a) many had produced long pollen tubes, while others showed 

 no signs of germination; the sugar solution was partly evaporated 

 and therefore was stronger than 5 per cent; (b) a very few had 



