40 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
micropyle and comes to lie between the integument and the peri- 
carp. In text fig. 2 the dotted line indicates in a schematic way 
the position taken by the embryo-sac under these circumstances, 
and text figs. 4 and 5 show two such embryo-sacs in detail. It 
is to be noted that the egg apparatus under these circumstances is 
always directed away from the funicle. In cases in which fertiliza- 
tion takes place, the egg elongates before 
division, and the embryo thus comes to lie 
within the ovule (text fig. 6). Fig. 7 serves 
as an example, although here the egg ap- 
paratus is not as far away from the micro- 
pyle as in many other cases. The habit 
of the embryo of producing a long slender 
stalk before division is constant, and may 
be seen even where the embryo-sac does 
not protrude from the micropyle, where, 
namely, the embryo-sac takes the same 
Fic. 6. One-celled embryo position as in the other Galicae (text fig. 7). 
vo ina protruding em- What the behavior of the pollen tube in 
FIG. 7. One-celled دی‎ this plant may be cannot be said, as no 
in embryo:sac occurring in the favorable material has so far been found. 
sore UAE posto A study of this point cannot fail to be of 
interest. 
The migration of supernumerary embryo-sacs into the funicle as 
above described is of special interest as it bears on the question 
of the guidance of the embryo-sac in its movements. 
Under ordinary circumstances the embryo-sac cell migrates 
down the micropylar canal, breaking through the thin cap o 
nucellar tissue. Where, however, the pressure of the integument 
is great enough the normal movements of the embryo-sac nucleus 
are prohibited, and the embryo-sac makes an irregular growth in 
any direction, and reaches no definite point. We may, there ore, 
conclude that the guidance of the embryo-sac into the micropylar 
canal is mechanical. 
The other species of Asperula studied show in general the 
same disturbances in the archesporium due to pressure as in 
Aspe rula montana, though not to the same degree. This is indi- 
cated by the fact that no exception to the normal position of the 
