On the origin of number and arrangement of the places of exit on the surface of pollen-grains

An observation on the pollen of Lythrum Salicaria, where beside the normal grains with three there also occurred grains with four places of exit, gave rise to this research. This phenomenon is also known to occur in other species; so investigators as Fischer (1890) and von Mohl (1834) mention a varying number of places of exit in the pollen of various species of plants belonging to different families. Besides pollen-grains with a varying number of places of exit may arise in case of irregularities of the reductiondivision, which Michaelis (1926) described for the pollen of Epilobium hirsutum. It is likewise known of a number of polyploid plants that the pollen possesses a greater number of places of exit than the pollen of the normal form, e.g. the diploid pollen-grains of the gigasforms of Solanum (Winkler 1916) and Oenothera (Boedyn 1925 —1928). Now the question rose in how far by this variability an insight could be gained into the way in which the arrangement of the places of exit is brought about in the pollen and what causes can play a part in the formation, the variation of number and the arrangement of these places of exit.