QUESTION OF INNER CAUSES IOI 
The general features of the change from a sporogenous to a sterile 
character are associated usually with a less dense protoplasm and a 
smaller and less marked nucleus. If disorganisation be the ultimate fate, 
the wall breaks down, and the identity of the protoplast is lost, with or 
without fragmentation of the nucleus, as in Pstlotum: or the proto- 
plasm may shrink and collapse, and the whole protoplast become 
highly refractive before the final absorption, as in angiospermic ovules. 
If the cell is to continue functional in a vegetative capacity, the changes. 
are those usual in cells passing from the embryonic to the mature condition. 
It has been stated above that the occurrence or absence of the tetrad- 
division, and of the consequent chromosome-reduction, is the ultimate 
criterion of distinction between a fertile and a sterile cell: in the majority 
of cases the distinction has been drawn on the basis of the results of 
subsequent development, not on that of actual observation of the nuclear 
changes. It is not, however, probable that this has led to any serious. 
errors, since the tetrad-formation which follows on chromosome-reduction 
is a sufficiently distinctive feature in all cases except in the ovules of 
Seed-Plants. This being so, it is not surprising that the most exact nuclear 
observations of sporogenous cells, in which the sterile or fertile development 
is a critical question, have been made on the ovules of certain Angiosperms, 
viz. in the case of the apogamous species of the genus Adchemilla.1 The 
exact questions connected with these plants do not come before us here ;. 
but in their.elucidation Strasburger had" reason to follow carefully through 
the development of certain embryo-sacs, as regards their nuclear condition. 
He found that an archesporial cell having entered the condition of an 
embryo-sac-mother-cell, its nucleus passes through the prophases of the reduc- 
tion-division, up to the stage of synapsis. The embryo-sac-mother-cell then 
alters its trend of development and becomes vegetative, and its nucleus 
passes out of the synapsis condition into that of a typical division, instead 
of continuing the reduction-division. The cell thus remains a part of the 
tissue-system of its parent, not the initial cell of a new generation. Such 
a case is interesting in that it shows how a cell may tremble on the verge 
between the sterile and the fertile state. It leaves, however, still open 
the question as to the influences, external or inner, which determine its 
fate. These probably vary in different cases, and the problem would 
naturally be a simpler one in the Homosporous Archegoniatae than in the 
ovule of an Angiosperm. It seems obvious in the simpler cases to suggest 
nutrition as one potent factor: it is a necessary axiom that an increasing 
spore-output, which is an advantage in increasing the probability of survival 
and dissemination, demands increased nourishment and protection: and 
that a vegetative system increased by sterilisation will tend to provide this. 
But still the advantage gained may be quite independent of the real 
cause: we are not yet in a position to translate the nutritive demand into 
terms of a direct influence upon the individual cell. It seems useless to 
1Strasburger, ‘‘ Die Apogamie der Eualchimillen,” Préngsh, Jahro., Band xli., Heft i. 
