112 
THE AMERICAN BOTANIST, 
portion of a flower, for in the majority of cases the flower 
bears both kinds of organs, it becomes attached thereto 
b3^ virtue of a viscous or gummy secretion w^hich holds it 
fast. This done the pollen grain bursts, and a slender 
tube issues from it which lengthens and traverses fine 
channels between the cells of the stigma until it reaches 
one of the embr3^o seeds at its base, which it at once fertil- 
izes, and thus renders it capable of perfecting and produc- 
ing a plant. Hence, it is clear that the longer the required 
tube the more material there must exist in the pollen 
grain, and the correlation is explained. 
We also see in this arrangement a bar to cross fertili- 
zation between unfitted plants, but another and less 
obvious bar exists in the fact that there is undoubtedly 
some sympathetic action upon the proper pollen grain by 
the viscous matter on the stigma which is lacking with 
alien pollen of the wrong species. Some extremely inter- 
esting experiments have been made in this direction by 
immersing pollen grains in solutions of this stigmatic 
gum, with, to some extent, very unexpected results, pollen 
grains sometimes reponding freely by bursting in quite 
foreign solutions, and yet failing in far more likely ones, 
though not of their own exact species. 
Such experiments are, of course, of great value to the 
hybridists, but have the drawback that the necessary 
length of tube formation is left out of the question, so that 
a pollen grain might quite well be induced, as it were, 
instantly to start form in its tube by misplaced stimulus, 
and yet be quite unable to penetrate the full length of the 
stigma, to say nothing of subsequent incompatibility as 
regards the intricate process of fertilizing the seed. Each 
embryo-sac or embryo-seed is only capable of being fertil- 
ized by one pollen grain, and when we see such a seed- 
vessel as that of the poppy, with its thousands of seeds, 
each individually and separately attached to the walls or 
compartment walls of the seed-vessel, and consider that 
at least an equal number of pollen grains, and probably a 
far greater number, become attached to the broad ribbed 
