274 
BOTANICAL GAZETTE [APRIL 
angiosperm, illustrating the important mechanism of this gameto- 
phytic selection. A mature cotton boll contains an average of from 
30 to 4o seeds, yet hundreds of pollen grains may germinate on 
Fic. 28.—Diagram 
of pistil of angiosperm 
having one ovule, show- 
penetrating conducting 
gametophytic selection. 
the stigma of the pistil. East (17) has deter- 
mined by actual count that there are usually 
1200 to 2000 pollen tubes in a single pistil in 
tobacco, sufficient to fertilize from four to six 
times the number of ovules in the ovary. 
Recent genetical studies have shown that 
this gametophytic selection in angiosperms 
represented by the pollen tubes has a signifi- 
cance of the first importance. For example, 
CorRENS (14, 15) has shown that in Melan- 
drium there is a selection between the male 
gametophytes in their race to. the ovules, that 
the female-producing pollen tubes are on an 
average decidedly faster in their growth than 
those carrying the factors which produce 
males. By applying much pollen so as to 
_ crowd the pollen tubes, he was able to increase 
the pollen tube competition in favor of the 
production of more females, and by sparse 
pollination he was able to stay this competi- 
tion somewhat, resulting in the production 
of more males than under normal conditions. 
This may be taken as definite experimental 
proof of gametophytic selection in angio- 
sperms. 
Experimental studies of pollen tube com- 
petition in angiosperms have been in progress 
for some time by the writer, and will be 
published in separate papers. It may be 
stated here that gametophytic selection, as 
it affects the evolution of angiosperms, is 4 
subject open to experimental study. It is already apparent that 
the genetic result of this gametophytic selection is a matter of the 
first importance if it relates to some of the heritable characters, 
