1915] HUTCHINSON—MALE GAMETOPHYTE OF PICEA 295 
Discussion 
1. Double pollen grains 
There are accounts of double pollen grains occuring in a number 
of species. Probably first was CHAMBERLAIN’s (10) description 
of Lilium tigrinum. ‘In about 20 cases there was a distinct wall 
dividing the microspore into two nearly equal parts.” Both cells 
contained starch. His fig. 20 shows one of the cells containing 
two nuclei ‘which seem to represent generative and tube nuclei.” 
One of the cells was regarded as prothallial, the other as antheridial. 
SCHAFFNER (11) found compound grains where two or more of the 
spores of a tetrad clung together (Typha latifolia). GuIGNARD (12) 
and Miss Pace (13) figure four microspores of an orchid within a 
common wall dividing to form tube nuclei and generative cells. 
COKER (13a) describes double grains in Larix europea. His fig. 6 is 
similar to my fig. 13; his fig. 8 corresponds to my fig. 12. He sug- 
gests that “the mother cell had only divided once, so that only 
two instead of four pollen grains were formed.”” In some of these 
grains “division proceeded as usual except that only one prothallial 
cell is evident”’ (cf. fig. 32). Poxtock (3) has described a number 
of variations in the pollen grain of Picea excelsa. ‘In the material 
examined, the proportion of double pollen grains was found to be 
2.4 per cent ina count of 1120. ‘The three or four cells lying along 
the dorsal side of the pollen grain of this type do not constitute a 
Prothallium or gametophyte of unusual size. They constitute 
the smaller portion of a pollen grain separated by a division wall 
into two nearly equal portions, each of which may form a typical 
antheridium.”’ Double pollen grains have been variously inter- 
preted. In Picea canadensis a study of the stages of development 
has shown that the two cells from which the double grain arises 
are the result of a primary division of the microspore (figs. 11, 13), 
and that one of these cells corresponds in origin to the more usual 
€vanescent cell. All gradations between an equal division and 
one which cuts off a lenticular evanescent cell have been found 
(figs. 6, 7, 10, 11, 13). In the double pollen grain of Picea one of 
the antheridial groups is homologous with the usual evanescent 
polar cell. 
