Holger Jorgensen: The Germination of the Pollen mass etc. 11 



in its whole length at once, it appears to be the separate grains of 

 pollen which gradually extend the chink. Sometimes one may also 

 find in the alar-chamber pollen-masses, which have as yet formed 

 only a tiny chink, through which a single pollen-tube has grown 

 out, even as the pollen-masses of certain Asclepiadeæ do not open 

 by a chink but by pores i. e. by several smaller chinks. 



Accordingly it is the pollen-grains of the projection only, which 

 form the chink. Now the question is, what qualities in these grains 

 of pollen are the cause of the chink. 



The thickness of the wall of the pollen-mass is the same through- 

 out the whole. It is true that the part of the wall of the pollen-mass, 

 in which the chink is formed, is dyed more quickly with aniline dye 

 than the rest, but also the very hard resinous appendages are dyed 

 very quickly with aniline dyes. Thus nothing in the construction 

 of the wall, as far as it is known, indicates that the part of the wall 

 of the pollen-mass, in which the chink is formed, should be weaker 

 than the rest of the wall. An explanation of the formation of the 

 chink founded upon a fact which cannot be proved is however 

 unsatisfactory, especially if some other explanation may be found. 



In the species Asclepias incarnata the chink is formed, as men- 

 tioned above, almost instantaneously on the pollen-mass being put 

 into water or into weak sugar-solutions, and immediately after the 

 formation of the chink the protoplasm of the grains of pollen which 

 form the chink is squeezed through it. But after the first burstings 

 have taken place, the bursting in the pollen-mass becomes weaker 

 and weaker, and eventually no bursting of any grain of pollen seems 

 to take place. Now it cannot be taken for granted that the outer 

 walls of the inner grains of pollen are stronger than those of the 

 chink-forming ones, and reacting against water and aniline dyes 

 in the same way as these. Now we must assume that the grains of 

 pollen which form the chink, at any rate in the beginning of the germ- 

 ination are able to apply a greater osmotic pressure than the rest 

 of the grains, and that the chink is due to this pressure, rather than 

 assuming differences in the strength of the walls to be the reason 

 of it. Moreover — in the case of A. cornuti as well as of A. incarnata 

 — the chink-forming grains of pollen, on the concentration of the 

 solution of sugar or of glycerine in which it is lying being intensified, 

 keep the greyish appearance, which is due to content of water, 

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



We have proved, first, that the formation of the chink is due 

 only to the pollen-grains of the projection of the pollen-mass, second- 

 ly, that there is nothing to indicate that the wall of the pollen-mass 



