﻿iqi6] ADAMS— POLLEN GRAINS 143 

 SERIES I 



May 22, 1913. — Pollen grains which were collected on May 19 

 were put into the incubator at 22 0 C. at 10: 25 a.m. Four cultures 

 were made, namely, (a) water, (b) 4, (c) 8, and (d) 16 per cent sugar 

 solution. They were examined at 4 : 20 p.m. the same day, with the 

 following results: (a) a small percentage had germinated, the 

 average length of the pollen tube being 66 . 8 /x; (b) a large number 

 had formed pollen tubes which were fairly straight, the average 

 length being 250.5 tx; one measured 317.3 /x; (c) a large number 

 had formed long pollen tubes, the average length being 634.6 ju; 

 (d) a large number had germinated and formed pollen tubes 668 fx 

 long or more. 



SERIES II 



June 6, 1 9 13. — Pollen grains which were collected on May 19, 

 were started in 8 per cent sugar solution at 4:00 p.m., the tempera- 

 ture of the laboratory being i5?5 C. They were examined at 3 : 50 

 p.m. on June 9, the temperature being 14? 5 C. Some had germi- 

 nated, one pollen tube being 434? 2 n long. 



SERIES III 



Pollen grains collected on May 19 were tested in 16 per cent 

 sugar on August 6, 1913, being examined on each of the two follow- 

 ing days, but none had germinated. 



Discussion 



As regards the most suitable medium for germinating pollen 

 grains, there is great diversity shown by different species of plants. 

 Some pollen grains when immersed in ordinary tap water swell up 

 and burst. This happens in Geranium sanguineum, Convolvulus 

 arvensis, Valeriana officinalis, and Scabiosa succisa, Martin 

 (5) states that the pollen of Trifolium pratense, T. hybridum, and 

 T. repens bursts almost instantly when dropped into water. He 

 found that the same thing happened in various sugar solutions. 

 His results obtained in germinating the pollen grains of Trifolium 

 were not at all uniform. He found that they germinated best on 

 wet parchment paper or hog's bladder, the amount of moisture 



