400 



IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



EFFECT OF TEMPERATURE ON GERMINATION. 



Table VI shows the effect of varying the temperature on ger- 

 mination of the pollen of the Wealthy, and the same was true 

 for the pollen of the other varieties. 



TABLE VI. 



EFFECT OF TEMPERATURE ON RATE OF GERMINATION' AND 

 GROWTH OF TUBES. 



Temperature 23° 



Time 3 hrs. 



Time 18 hrs. 



TEMPERATtTRE 10° 



Temperature — 1.5° 



Water 



2V2 per cent sugar so. 



5 per cent sugar so. 



10 per cent sugar sol. 



Membrane 



1/20-1/lOmm. 



From table VI it is seen that low temperatures retard germi- 

 Tiation but do not prevent it, even at — 1.5° C. With more time 

 allowed the percentage of germination at — 1.5° would very 

 likely have been greater. In accord with the results of other in- 

 vestigatoi'S, the pollen was found to be exceedingly resistant to 

 cold. Pollen kept frozen up solid in water and sugar solutions 

 for three or four hours gave a normal percentage of germination 

 when its germination capacity w^as tested, thus showing no bad 

 effects from cold. 



PISTIL. 



THE NATURE OF THE STIGMA. 

 The stigma is papillate as shown in figure 165. At the open- 

 in"- of the flower the paplll* have reached tneir full develop- 



