420 
IOWA ACADEMY OP SCIENCE Vol. XXIV, 1917 
when water was added to the mount. The turgid grains measured 
twenty-three by nineteen microns. 
ABNORMAL POLLEN. 
Certain of the. mother cells in the collections of September 16, 
1914, developed abnormally. Usually each of these produced a 
single giant pollen grain. 
The anlage of the abnormal grains could usually not be de- 
tected until after the heterotypic and liomotypic divisions. The 
four nuclei resulting from these divisions take the usual arrange- 
ment. But instead of forming into a tetrad of spores the whole 
group with the surrounding cytoplasm becomes enclosed by a 
new wall which begins to form inside the wall of mother cell 
(21, Plate XIV). One of the nuclei now increases in size while 
the other three degenerate. The latter generally lie at one side 
and in late stages are crowded out against the wall. They often 
fuse together (22 and 23, Plate XIY). Meanwhile the dominant 
nucleus has enlarged until it has attained a diameter of twelve 
microns. The normal spore nucleus at first measures four and 
five-tenths microns. The increase in the case of the normal nu- 
cleus is four-tenths the original while in the abnormal grains 
the increase is sixteen-tenths. The wall of the giant microspore 
is of about the same thickness as the wall of the normal pollen 
but no exit pore is visible. The shapes of the giant grains vary 
from spherical to irregularly lobed (23, 26, 27 and 28, Plate 
XIY). 
The ultimate fate of the persistent nucleus was not deter- 
mined. One giant grain was found in which two nuclei much re- 
sembling the tube and generative nuclei of the normal pollen 
occurred (24, Plate XIY). A dark crescent at one side may 
have represented the three degenerating spore nuclei. 
The largest of the grains was thirty-five microns in diameter. 
The volume was therefore five and five-tenths times that of the 
ordinary pollen grain. Whether or not the giant grains are 
capable of germinating is of course unsettled since none were 
found except in the fixed material. 
Some of the variations from the above procedure in the devel- 
opment of the abnormal pollen were the following. In some 
cases the nuclear divisions of the mother cell were delayed for 
some time as evidenced by the thickened wall and the presence 
