1899 | LIFE-HISTORY OF LEMNA MINOR 55 
integuments grow much more rapidly than on the other, so that 
when the ovule is fully formed the embryo sac lies perpen- 
dicular to the stalk of the ovule (figs. 9, ro, g2), and in a 
Wea 
ant 
4| 
Fic. 40. Nucellus with dividing archesporial cell ; at each side the beginning of 
the carpel; at rim of nucellus the beginning of first integument. X 1375. 
Fic. 41. Nucellus, with megaspore, tapetal cells, and beginning of integuments. 
x 1375. 
plane parallel to the surface of the frond, with its micropylar 
end toward the base of the frond. It must be borne in mind 
that while the ovule when young was orthotropous, and gradu- 
ally became half anatropous, 
the carpel has also changed 
from an upright position to 
one which is prostrate. Thus 
the position of the ovule has 
constantly changed in two 
directions during growth, 
making it extremely difficult 
to obtain sections showing 
the successive stages in the 
growth of the carpel, ovule, 
and embryo sac. This diffi- 
i eee ee: 
preciated when it is remem- Rea be Kaley iis x 890. / 
bered that the flowers are so. 
small that it is impossible to orient them, or to determine their 
respective ages except under high magnification. As a result 
of these conditions most of the hundreds of series of sections 
made were of no great value. 
