Holger Jorgensen: The Germination of the Pollen-mass etc. 13 



mention Gager (5), who likewise used a 5 per cent cane-sugar solu- 

 tion and slices of sugar-beet, but did not follow the development 

 of the pollen-tubes in culture beyond the very first stage. On the 

 pollen-masses of other species of Asclepias we have a quite short 

 paper by Halsted (6). According to Halsted the pollen-masses 

 of these species germinate in cane-sugar solutions, the concentra- 

 tions of which are between 1 and 100 per cent, and best in a middling 

 concentration, e. g. at 65 per cent in the case of A. verticillata. In 

 Halsted as well as in Brown a further statement as to what is 

 meant by a good germination is wanting. Most probably it means 

 that the pollen-tubes grow out from the pollen-mass and attain to 

 a considerable length. I shall use the term "good germination" to 

 denote the above-mentioned conditions. 



Presumably the experimenters, mentioned above, cultivated 

 their pollen-masses in rather big cups, that is, in a considerable 

 quantity of liquid. This is a mode of cultivation, which comes natu- 

 ral, when one has to do with these rather big objects, and in the 

 case that we are concerned with, the determination of the concen- 

 tration, by which the best germination comes to pass, we thus pre- 

 vent the pollen-masses from altering the concentration of the solu- 

 tion by themselves. 



I myself began by cultivating pollen-masses in the following 

 way: I placed a chance number in 10 or 25 c. c. of nutrient solution, 

 and as such was used cane-sugar solutions of different concentra- 

 tions. The only constant result arrived at through such experiments, 

 is that the pollen-masses are able to germinate in cane-sugar solu- 

 tions, the concentrations of which are between 5 and 35 per cent. 

 Otherwise the results vary. Now the germination is best at 20 per 

 cent, now at 30, and again at 35 per cent. Sometimes the pollen- 

 tubes are at these concentrations strongly twined, at other times 

 all the tubes of pollen remain inside the pollen-mass as they do at 

 the low concentrations at which germination takes places. On exami- 

 ning the contents of a pollen-mass, which has been germinating for 

 some days in a 5 per cent solution all the grains of pollen will be 

 found to have germinated, but the pollen-tubes to have burst 

 because of some part of the protoplasm having been squeezed out 

 through the end. The matter which Corry observed in front of the 

 chink of the pollen-mass thus consisted of protoplasm which had 

 been squeezed out. Before leaving these experiments of culture I 

 shall only mention that the pollen-tubes from one pollen-mass in 

 the different solutions are often found to have grown into another, 

 and vice versa. 



