16 Dansk Botanisk Arkiv, Bd. 2 Nr. 10. 



consists in the liquid, in which the pollen-tubes are growing, altering 

 its concentration quite steadily from a lower to a higher concentration. 

 II. Further, the pollen-tubes are stimulated positive chemotropic by 

 cane sugar. Thus the twinings which often result on the pollen- 

 masses germinating in greater quantities of liquid are explained — 

 in the case of A. incarnata I have seen pollen-tubes branch out in 

 the end, — and thus it may also be explained that pollen-tubes in 

 pollen-masses, germinating in greater quantities of liquid, remain 

 inside the pollen-mass, or return to it after having grown outside 

 the chink, as these great pollen-masses are able to produce them- 

 selves an alteration of the concentration in their own interior, and, 

 finally, that pollen-tubes from one pollen-mass so readily grow into 

 another pollen-mass. 



Pollen-masses are able to germinate at a higher concentration 

 in pendant drop than in greater quantities of liquid. Pollen-masses 

 germinating at such a high concentration in pendant drop, e. g. at 

 50 per cent, send forth pollen-tubes just as long as at lower con- 

 centrations, and the whole type of germination is the same, only 

 the germination proceeds a little slower. It must here be taken for 

 granted that the pollen-mass at first burns the sugar till the con- 

 centration in the pendant drop has been reduced to the value at 

 which the germinatinon can begin. 



In Asclepias, and no doubt in the Asclepediaceæ upon the whole, 

 the pollen-tubes may be pulled out of the style, as they come out 

 together with the pollen-mass, from which they issue, on the latter's 

 being taken out. What may be learnt in this way about the pollen- 

 tubes and the fluid of the style corroborates the view, which we 

 have advanced aboye of the reason for the growth of the pollen- 

 tubes, short pollen-tubes in the style proving to be surrounded 

 by a rather thin liquid, while the longest pollen-tubes, which we 

 are able to take out, are surrounded by a very dense liquid. More- 

 over the pollen-tubes in the style never twine. 



Our experiences of the germination of the pollen-mass of Asclepias 

 justify our criticizing the works by Molisch and others, whose task 

 has been to describe the conditions of the germination of the pollen- 

 grains and the growth of the pollen-tubes, for in none of them due 

 allowance has been taken to the fact that the grains of pollen and 

 the pollen-tubes may alter the surrounding liquid. At any rate in 

 the case of two species, viz. Campanula rotundifolia and Linaria 

 vulgaris, I have succeeded in proving that germination of pollen- 

 grains and growth of pollen-tubes only take place when many 

 grains of pollen are accumulated in the nutrient solution. If the pollen- 





