532 Journal of Agricultural Research voi. xvni, no. lo 



provided its moisture content does not reach a dangerously low level. 

 Normal pollen is shown in Plate 6i, A. The same pollen exposed for 2 

 minutes to the air is shown in Plate 61, B. Some of this pollen may 

 germinate. As previously stated, however, when the pollen was exposed 

 to the air for 10 minutes, it had lost its germinative properties completely. 

 This shrunken pollen, when applied to the stigma, affected the stigma 

 hairs noticeably. The pollen grains took up moisture, attaining the round 

 appearance of normal pollen; but the stigma hair cells lost their turgor and 

 became vacuolized. It was thought that this effect upon the stigma hair 

 cells might be overcome by swelling the pollen previous to its application 

 to the stigma, but pollen so treated did not germinate. 



Since the viability was lost so quickly in free air, it was obvious that 

 more elaborate experiments of this nature were useless. While not 

 strictly in free air, pollen remained viable 24 hours in a cool, dark room, 

 when inclosed in a loose Van Tieghem cell with a piece of pea leaf as a 

 moisture-giving medium. 



POLLEN KEPT OVER SULPHURIC ACID 



The trials in free air indicated that the regulation of the moisture con- 

 tent of the air was perhaps the most important factor in preserving pollen. 

 Pollen was kept over sulphuric acid of different concentration as follows : 



15.14 per cent with a 90 per cent moisture saturation; 



37.69 per cent with a 60 per cent moisture saturation; 



54.00 per cent with a 30 per cent moisture saturation. 



Germination was later secured only from the 90 per cent moisture 

 concentration. The experiment was not satisfactory in that the control 

 was not accurate. This was especially true of the temperature. From all 

 the observations made, it is the opinion of the authors that in the presence 

 of a considerable range of humidity, pollen must remain viable for some 

 time at a temperature of about 10° C. 



POLLEN KEPT IN VACUA 



The consequence of exposing pollen to the air were so obvious that 

 experiments in vacua seemed foredoomed to failure ; but citrus pollen 

 had been preserved so successfully in this way that the same method 

 was employed with barley pollen. 



The pollen was put in gelatin capsules, care being taken not to have 

 them completely closed. The capsules were placed in test tubes, which 

 were subsequently evacuated, the vacuum being regulated to the millimeter 

 pressure wanted. In no instance did barley pollen remain viable. The 

 pollen was invariably shrunken and would not germinate under any 

 conditions. 



