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



pollen-tubes, and that the rising of the concentration which the 

 pollen-tubes of the different plants require is different, the results 

 of Strasburger would receive a simple explanation. 



Results. 



I. 



1. It has been proved to be likely that the pollen-grains, in 

 the free outer-walls of which the chink of the pollen-mass in Asclepias 

 cornuti and A. incamata is formed, are able to become more turgid 

 than the rest of the grains of the pollen-mass. By this the formation 

 of the chink would be explained in the most natural way, as no 

 other reasons for the formation of the chink are to be found. 



2. The part of the wall of the pollen-mass, in which the chink 

 is formed absorbs aniline-dyes more quickly and allows these and 

 water to pass more quickly through itself than does the rest of the 

 wall of the pollen-mass. 



3. The wall of the pollen-mass assumes in strong sulphuric 

 acid a deep red colour, which disappears in dilute sulphuric acid, 

 in water, and in alkali. In alkali the wall of the pollen-mass gets 

 brown. This colour disappears again in water and in dilute acids. 



II. 



1. The pollen-mass of Asclepias cornuti is able to germinate 

 in cane-sugar solutions of different concentrations, but different 

 according as the quantity of liquid is great or small in proportion 

 to the cubic-contents of the pollen-mass. The pollen-mass ger- 

 minates best in small quantities of liquid, the concentrations of 

 which are between circa 20 per cent and circa 30 per cent. As the 

 pollen-mass presumably makes the concentration of the small 

 quantity of liquid rise, and as no other alteration of the liquid can 

 be found, the difference of the germination in a great and a small 

 quantity of liquid is most probably due to, that the pollen-tubes 

 in order to grow require that the concentration of the nutrient 

 solution rises steadily and at a certain rate. 



2. The conditions of the pollen-tubes placed under different 

 conditions of culture give reason to assume that the pollen-tubes 

 are positive chemotropic to cane-sugar. 



3. From out of the style of the plant, pollen-tubes of various 

 lengths may be taken. Short pollen-tubes prove to grow in a thin 



