16 
2°. The process of embryosac-formation may be affected by 
reduction. Instead of four, only three or two megaspores 
are formed, or even the embryosac-mothercell itself func- 
tions as megaspore. Thus chromatine-reduction, ordinarily 
occurring during embryosac-formation, necessarily is trans- 
ferred to a later stage. “Bei teilweiser Unterdriickung der 
Tetradenteilung wird der zweite Teilungsschritt der Reduk- 
tionsteilung in die keimende Spore verlegt, und bei voll- 
stindig ausbleibender Tetradenteilung finden beide der zur 
Reduktion notwendigen Teilungen innerhalb der keimenden Ma- 
krospore statt.« (S. 27). 
. The process of embryosac-development is wholly independent 
of that of embryosac-formation. Among Liliaceae e.g. all 
types of megaspore-formation are found, from the normal | 
tetrad down to total suppression. Always however the func- 
tioning megaspore — by three divisions — reaches the 8- 
nucleate stage. 
. The process of embryosac-development is determined by the 
number of divisions, by the arrangement of the nuclei, b 
_ vacuolation and by cell-formation. . 
- On these grounds Exnst, when reviewing the literature, con- 
cludes that two types of embryosacs can be recognised, viz. the 
ordinary eight-nucleate one and a sixteen-nucleate type, “als 
‘dltere oder doch als selbststandige Form des Embryosackes der 
Angiospermen* (S. 29). This more primitive type is distinguished 
by the divisions numbering four instead of three, by the ab- 
sence (at least at first) of a central vacuole, and by the lack 
of bipolarity. The 16-nucleate sac thus shows itself to be of a 
primitive character as to embryosac-development, and of a 
reduced nature as to embryosac-formation, there being no row 
at all, the embryosac-mothercell itself functioning as embryosac. 
we 
° 
be 
oO 
This marked distinction between embryosac-formation and 
development is a real advantage on Counrer’s system. It is @ 
first step on the way of treating the various processes of the 
female gametophyte separately . So far it opens the prospect 
of getting a natural system. Laying all the stress however on 
1 
a 
