16 IOWA STUDIES IN NATURAL HISTORY 
conditions reported in Polypompolyx by Lang (6). Develop- 
ments are similar except that the receptive tissue into which the 
micropylar haustorium enters is located in a hump on the fun- 
iculus of the ovule instead of in the placenta. The outgrowth 
is dominated by the endosperm and it displays characters simi- 
lar to that described above for the Bladderwort, except that it 
never attains the prominence shown in Utricularia, and is less 
conspicuous than the antipodal haustorium of the same ovule. 
Since both masses of receptive tissue are within the ovule in 
Polypompholyx, it must use its funiculus in the regular way 
and so is debarred from the unusual achievement of Utricularia 
which attacks the placenta directly. 
The writers of this paper would like to emphasize the view 
that events taking place within the pistil of the Angiosperm 
are so closely inter-dependent that these relations dominate the 
gametophytes. They prevent, on one hand, enlargement of the 
female gametophyte in any such degree as marks the Gymno- 
sperms, since fertilization is not long delayed. Perhaps these 
same conditions also operate in some way to inhibit reduction 
of the embryo-sae to the theoretically possible limit of a single 
egg, by demanding codperating cells and nuclei. The male 
gametophyte, as represented by the pollen tube, presents a simi- 
larly specialized mechanism. It must, with the female gameto- 
phyte, follow a precise program involving both time and space 
relations which permit of limited variation. 
In other words, the make up of the ovule and its contents in 
relation to the pollen tube habit outweighs all other factors 
and invites to a peculiar type of specialization. The limitations 
imposed by the associated parts are very definite, and despite 
the most marked contrasts in size, habitat, floral and vegetative 
development, as well as divergent kinship between the various 
groups of Angiosperms, the behavior of the male and female 
gametophytes displays a remarkable uniformity. This con- 
stancy then represents a survival of structures and habits best 
fitted to the exacting type of siphonogamy found in this great 
group, rather than a stage of incomplete reduction or evolution. 
SUMMARY 
1. The inverted ovules of Utricularia vulgaris are crowded 
