28 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
a mixture of cells it is not easy to distinguish this cell, especially 
as it often happens that several pass through the initial stages of 
migration, and the result is very confusing. I have, however, with 
reasonable certainty, been able to pick out the most active cell, as 
in figs. 4 and 5. The embryo-sac cell, so far as determined, may 
arise out of any of the megaspores, so that we may regard these 
for the greater part as physiologically equivalent. The appear- 
ances presented by the archesporium at this time match closely 
those seen in Alchemilla as described by Murbeck.* Tapetal 
cells are not formed. 
No starch is seen in the integument until the migration of the 
megaspore, when a slight accumulation occurs, evenly distributed 
throughout the whole. During the maturing of the embryo-sac, 
the amount of starch increases in a zone surrounding it. As the 
endosperm starts to grow, zonal accumulation disappears and a 
general distribution is again seen which becomes gradually more 
pronounced in the peripheral parts. 
THE DEVELOPMENT OF THE EMBRYO-SAC 
One of the megaspores which have developed as described 
above commences to enlarge and to migrate along the micropylar 
canal. This takes place when the ovule is well developed and has 
taken on its mature form. 应 5, fig. 4, shows these conditions 
just previous to the migration of the megaspores. It not infre- 
quently happens in this species that two or even three megaspores 
commence to migrate at the same time and take paths which are 
nearly parallel. In such cases a good deal of confusion arises, 
which makes it difficult to interpret properly the preparations 
showing this condition. The remaining megaspores retain their 
character for some time, some degenerating more rapidly than 
others, and the resulting mass adds not a little to the difficulty of 
making out clearly what one sees. Occasionally two of the mi- 
grating megaspores germinate, although in no cases which I have 
observed has development passed beyond the four-celled stage 
(Pl. 5, fig. 8) in any but the more advanced and normal one, 
which is set apart as the fundament of the functional embryo-sac. 
* Murbeck, Sv.  Parthenogenetische ها زیون‎ in der Gattung Alchemilla. 
Acta Reg. Soc. Physiogr. Lund, 11 : 1- -47. 1901. 
