1897 | LIFE HISTORY OF LILIUM PHILADELPHICUM 423 
IL 
THE POLLEN GRAIN. 
CHARLES J. CHAMBERLAIN. 
(WITH PLATES XXXV-XXXVI) 
It is not my purpose to treat this subject in any detail, but 
merely to note a few of the more essential and critical points. 
Thanks are due to Professor Coulter for his criticism, and to 
many advanced students in the laboratory for the privilege of 
€xamining several hundred preparations. 
HISTORICAL. 
During the past thirty years the embryo sac of spermato- 
phytes has received large attention, and its main structures 
have been figured and described in many species, but the pollen 
grains, which are of equal importance, have received but scant 
attention. The most important literature has been furnished 
by Hartig, Elfving, Dixon, Guignard, Farmer, and Belajeff. 
Hartig was the first to describe two nuclei in the ripe pollen 
grain. Strasburger (1884) greatly extended the researches and 
described the pollen grains of a great variety of species represent- 
ing the principal groups of angiosperms and gymnosperms. He 
showed that the smaller of the two cells in the ripe spore is the 
generative, also that the generative nucleus undergoes division, 
giving rise to two male nuclei. This division usually takes 
place in the pollen tube, but in many cases it takes place in the 
Spore, so that the mature spore may contain three nuclei. Elf- 
ving saw three male nuclei in the mature spore of Andropogon 
campestris. Strasburger (1884) reports the occurrence of four 
male nuclei in the pollen tubes of Ornithogalum and Scilla Guig- 
nard (1891) says that in Lilium Martagon the division of the gen- 
ae €rative nucleus occurs only in the pollen tube, and that the tube | 
_ nucleus never divides at all. ‘Strasburger (1884) also” makes 
oe pe general statement that. the tube nucleus never ¢ divides. 
—as ee = a _ ee —— spe ccd with a a 
