1900] DEVELOPMENT OF THE EMBRYO-SAC 37 
disintegration. It seems therefore that in this case the two 
sperm cells never separate. At this stage the wall which 
separates the egg from the rest of the embryo-sac is prominent, 
and can easily be seen to inclose the synergids as well. Camp- 
bell found both sperm nuclei entering the embryo-sac in Naias 
but only one in Zannichellia. Schaffner found that in Sagittaria 
one always remained in the pollen tube. 
THE EMBRYO. 
The classical investigations of Hanstein? and Famitzin* on 
the development of the young embryos in both monocotyledons 
and dicotyledons have made us familiar with the process in a 
large number of plants. The work of later students has only 
gone to confirm the results reached by these investigators, at 
least as regards general features. However, the results obtained 
from certain monocotyledons by Schaffner and later by Campbell 
seem to be at variance with those above mentioned ; and as bear- 
ing upon this point Potamogeton becomes of interest. 
In Potamogeton the fertilized egg nucleus remains for a very 
short time in the resting condition, perhaps it divides immediately, 
but lack of spindles in the young embryos made it impossible to 
determine this. Immediately after the first division, the basal 
cell undergoes a change whereby it becomes gradually larger 
until a size several times the original is reached. At this stage 
the cell is a very striking object (figs. 24, 26). The very large 
vacuole, which soon appears, at length forces the nucleus to the 
bottom of the cell where it henceforth remains, while the nucleus 
itself undergoes considerable enlargement. Just behind this 
large nucleus of the basal cell, one can often see a synergid, even 
as late as the several-celled stage of the embryo. 
The basal cell never undergoes division, but on the contrary 
remains for a long time in its enlarged condition attached to the 
end of the embryo-sac. But sometimes during the later stages 
9 HANSTEIN : Die Entwickelung des Keimes der Monokotylen und Dikotylen. 
_ Bonn, 1870, 
*°FAMITZIN: Embryologische Studien. Mém. de l’Acad. Imp. Sci. de St. Petersb. 
VUI. 26:—. 1879. 
