HoJger Jørgensen: The Germination of the Pollen-mass etc. 17 



grains of these two species are placed separately or few together in 

 pendant drop it is impossible to make them germinate at any con- 

 centration; but the pollen-grains of both these species are able to 

 germinate and send forth long pollen-tubes, when a great number 

 are accumulated in a very small pendant drop of a weak cane-sugar 

 solution (e. g. 1 per cent). A fact which in this case also indicates 

 an alteration of the concentration as being the reason of the ger- 

 mination and the growth is that only a percentage of the grains 

 of pollen germinate 1 ). 



Most probably what has now been asserted in the case of As- 

 clepias cornuti and the two above-mentioned species will prove to 

 be true in the case of more plants. This I infer partly from the re- 

 marks often met with in the literature that the germination of the 

 grains of pollen is capricious, partly from a remark by Elfving(7). 

 The latter used for his experiments weak sugar-solutions and re- 

 marks about the final fate of the pollen-tubes in culture as follows: 

 In all the cultures the pollen tubes eventually swelled in the end 

 and decayed by bursting. 



Molisch (4) and others have in the case of the pollen-grains 

 of various plants stated the concentrations of sugar at which the 

 best germination takes place, and the limits within which germina- 

 tion is possible at all. These concentrations prove to be different 

 for the different plants. Perhaps one may draw the conclusion from 

 these figures that the rising of the concentration, required by the 

 different pollen-tubes in order to develop normally is different for 

 the different species. This would agree very well with the results, 

 Strasburger (8) arrived at, through his experiments in the way 

 of germinating upon the stigmas of other species of the pollen- 

 grains of different species. 



Strasburger found that the pollen-grains of many species 

 are able to germinate on the stigmas of other plants and to send 

 shorter or longer pollen-tubes into the styles. This seems to imply 

 that it is not reasonable to take so great qualitative differences 

 for granted between the style-liquids of the different plants, as 

 experiments in culture by Molisch (4), Lidforss (9) and others 

 implied. Assuming that a rising of the concentration takes place 

 in the style-liquid, different for the styles of different plants, that 

 this rising of the concentration is necessary to the growth of the 



In Campanula rotundifolia the pollen-tubes often grew from the drop 

 into the air. Such tubes were not attracted by ovules placed in the 

 damp chamber, perhaps because the ovules are here separated from 

 the plant. 



