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



Besides, the rapid penetration of fluids into the pollen-grains 

 of the projection may be proved in another way. Pollen-masses are, 

 immediately on being taken out of the flower, yellow to the naked 

 eye, owing to the colour of the wall of the pollen-mass ; but under 

 the microscope they prove to be greyish and opaque. Their greyish 

 appearance is due to the water in the pollen-grains, for on remaining 

 exposed to the air the greyish appearance is lost ; it reappears however 

 on the pollen-mass being placed in a vessel saturated with vapour. Desic- 

 cated pollen-masses appear to be yellow also under the microscope, be- 

 sides being pellucid, owing to an oil in the grains of pollen. If a desicca- 

 ted pollen-mass is put into water or in a vessel sa- 

 turatedwith vapour, the pollen-mass is seen under 

 the microscope to become greyish, first where 

 the chink is later on formed, and the greyish 

 appearance from there to spread into the pol- 

 len-mass. 



Thus liquids are proved to penetrate most 

 rapidly into the grains which are lying just 

 inside the chink, and to penetrate from here 

 quickly into the other grains of the pollen-mass. 

 Further it is shown that the difference in pene- 

 trability in the different parts of the wall most probably is related 

 to a difference in the chemical nature ; but by this the cause of the 

 formation of the chink has not been found; for we must here 

 emphasize that the chink of the pollen-mass in Asclepias cornuti 

 when being upon the stigma or in strong sugar solutions, is not 

 made until long after the surrounding liquid has penetrated into 

 the pollen-mass, so that all the grains are able to become turgid 

 before the chink is formed. So the formation of the chink cannot be 

 due to the fact, that the chink-forming grains of pollen become 

 turgid before the rest of the grains of pollen. 



The joint pressure of the grains of the pollen-mass is of no- 

 consequence for the formation of the chink. Sections of pollen- 

 masses containing the chink-forming grains of pollen, form the chink 

 in sugar-solutions and do so as quickly as an uninjured pollen-mass 

 (vid. Fig. 3 A). It must however be added that the sections, if very 

 small, form no chink (vid. Fig. 3 B). Moreover the chink is not formed 



in strong sulphuric acid. In pollen-masses, which have been lying in 

 strong sulphuric acid, and are then placed in bases, the deep red co- 

 lour first goes, and then the reddish-brown base-colouring appears. 

 Molisch (4) has discovered that the extine of the pollen grains of cer- 

 tain Compositæ are dyed a deep red with concentrated sulphuric acid. 



