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



should be weaker in the place where the chink is formed than the 

 rest of the wall, — finally it' has been shown to be probable that 

 between the chink-forming grains of pollen and the rest of the 

 grains of the pollen-mass there is the difference that the chink- 

 forming grains of pollen at any rate in the beginning of the germina- 

 tion are able to apply a greater osmotic pressure than the rest of 

 the grains. 



An inner differenciation in the pollen-mass corresponding to 

 the differenciation of the wall of the pollen-mass was to exist accord- 

 ing to this theory. The pollen-grains of the projection were to be 

 distinguished not only by their walls absorbing water and aniline- 

 dyes rapidly, but also by being able themselves to become more 

 turgid than the rest of the grains of the pollen-mass. 



The explanation of the formation of the fissure given here is 

 founded upon the acceptance of a fact to be met with elsewhere in 

 the vegetable world. Lidforss (9) and others have pointed out in 

 the case of several plants that on the grains of pollen from the same 

 anther being placed in water, a certain percentage of the grains of 

 pollen burst, while the rest do not become so turgid as to burst, 

 and it must here be called in mind that at any rate in the cases 

 where the bursting comes to pass by the protoplasm being squeezed 

 out through the germ-pores differences in the strength of the exine 

 cannot possibly be of any consequence. In the two species of Asclepias 

 with which we are here concerned, the pollen-grains that are able 

 to become most turgid were then to form the projection of the 

 pollen-mass. 



B. 



The Germination of the Pollen-grains and the Growth 

 of the Pollen-tubes. 



Robert Brown (2), who is the first to have studied the germ- 

 ination in culture of the pollen-mass of Asclepias cornuti, found 

 that the pollen-mass is able to germinate well upon the stigma of 

 Orchis, but badly in dilute sugar solutions. Corry (3) for his experi- 

 ments in germination used 5 per cent cane-sugar solutions, and found 

 that the germination proceeds badly by a concentration of that 

 sort, and that in front of the chink a viscid matter is formed, through 

 which a few pollen-tubes grow out. By way of completeness I shall 



