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374
william rosén
Fig. 1. Aolana acuminata. Young ovule. X 100. - Fig. ’1. Nolana humifusa. Ovule
with mature embryo-sac. X 100. — Fig. 3—6. Ditto. Stages in development of the
embryo-sac. X -100. — Fig. 7. Xolana paradoxa. Mature embryo-sac. X 400.
(Fig. 9). By Ihe third division in each of the two micropylar cells
another longitudinal wall follows al right angles to Ihe first one. In Ihe
two lower endosperm cells longitudinal walls are formed, too. From
this moment it has been difficult lo follow Ihe divisions in particular.
1 have seen that transverse walls are formed but not synchronously.
1 have not been able to decide whether or not the four micropylai cells
undergo further divisions by formation of any transverse walls. In one
of my preparations 1 certainly think that one transverse wall formation
has taken place. Bid anyhow, further longitudinal walls are not formed
in these four cells surrounding the zygote. Soon I hey assume Ihe shape
of synergids and Ibis appearance they maintain a fairly long time. In
Fig. 10 is drawn a not very early endosperm stage. Only two of the
four micropylar cells are visible, but their synergid-liké shape is
conspicuous. Later on when the zygote has began to divide Ihe vacuol
disappears and Ihe dense cytoplasm occupies the whole cell and is
deeply stained by haematoxyline (Fig. 11). Owing lo this they are quite
different from Ihe resl of endosperm cells. The synergid-like shape can
not be interpreted as an anomaly due to Ihe fixative or lo other
solutions used, because of the regularity of its occurring in young
endosperm stages and because of no endosperm cell else is seen lo be changed
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