1899 ] LIFE-HISTORY OF LEMNA MINOR 53 
the resulting nuclei being also smaller (jigs. 35, 39). By the 
time these divisions have been completed the outer spore wall is 
quite heavy, and is covered irregularly with spiny outgrowths. 
36 37 
Fics. 26-29. Formation of tetrads. X 1375. 
Fic. 30. Microspore in which the nucleus indicates approaching germination 
38 
Fic. 31. First division of the wee of the microspore; granules at ends of 
spindle and in adjacent cytoplasm. X 24 
G. 32. Same as fig. 37. Position si quibie which places one daughter nucleus 
near wall of spore. 2400. 
Fics. 33-37. Microspores after first division of nucleus; one cell placed near the 
wall. X 1375. 
Fic. 38. Microspore with generative cell dividing. X 2400. 
Fic. 39. Same as fig. 38, showing male cells. X 2400 
No indications of thinner regions of the spore wall, especially 
developed to facilitate the escape of the pollen tube, could be 
found. 
Before this time the tissues separating the two loculi on each 
side have broken down, forming the two pollen sacs. These 
break open and the spores float out upon the water. The micro- 
Spores of the two anthers are not in the same stage of develop- 
ment at the same time. When the mother cells of the older 
anther are beginning to divide, the corresponding cells of the 
younger anther are just becoming free in the mucilaginous 
material of the broken down cell walls and tapetum. Conse- 
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7 
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