526 Journal of Agricultural Research voi. xviii, no. 10 



Tieghem in 1869 (ii) used an artificial medium. Jost (2), studying the 

 physiology of pollen, concluded, from the fact that it germinates on the 

 stigmas of other plants, that physical factors and not specific substances 

 of the stigma were responsible for germination. 



Jost (5), working with the pollen of Glyceria, Dactylis, and Secale, 

 accidentally noticed in one of his experiments that pollen of these plants 

 would germinate in close proximity to a drop of water. He was able 

 thus to germinate the pollen of rye {Secale cereale) without any medium 

 whatsoever. 



Mangin (7) concluded that pollen of certain plants could germinate 

 and grow from the food reserves within the pollen grain, while pollen of 

 other plants did not grow well except in the presence of external nutrients, 



EXPERIMENTS WITH SOLUTIONS 



In the experiments of the authors the first trials of germination were 

 made in water and solutions of sugar, agar, and other nutritive sub- 

 stances of various osmotic concentrations. It is unnecessary to report 

 more of the aqueous tests than the behavior in sugar solutions. High 

 concentrations resulted in plasmolysis. Low concentrations resulted in 

 bursting in mature pollen. Immature pollen grains increased in size 

 but did not burst. Mature pollen did not increase in size before bursting. 

 In concentrations slightly less dense than those at which plasmolysis 

 begins, small knobs were formed by the protrusion of the cell contents from 

 the pore through which germination takes place. These knobs reached a 

 length of from 2 to 4 /i but did not grow further. The knobs frequently 

 were distended by continued absorption of water. If the water absorp- 

 tion is rapid, the bulging intine, which surrounds the extended cell con- 

 tents, is ruptured before the knobs attain much size. Various stages of 

 knob formation are shown in Plate 60. 



EXPERIMENTS WITH MOIST CHAMBERS 



When it became evident that germination was not likely to be secured 

 in solutions, trials were made on various membranes of plant and animal 

 origin. These experiments met with no success. Trials were made in 

 moist chambers with and without membranes. The moisture in these 

 chambers was supplied sometimes by drops of free water and sometimes 

 by fragments of living plant tissue, the necessary humidity in the latter 

 case arising from the evaporation from ruptured cells. No germination 

 was obtained. If the cells became too moist, the pollen burst; if they be- 

 came too dry, the pollen shrank. 



The water adjustment of the pollen was so delicate that it seemed im- 

 possible to obtain a method of sufficient refinement to secure and main- 

 tain the proper conditions. If was found that the pollen on a slide could 

 be readily killed, drowned as it were, by blowing one's breath upon it. The 

 final success came from an observation the senior author made at Aber- 



