Notes. 
619 
segmentation underlying the existence of that cell or cells which a 
last analysis may mark out as the ‘ archesporium ’ ; nor do these 
ultimate parent-cells give rise in all cases to cognate products. 
Therefore it is concluded that the general application of a definite 
term to those ultimate parent-cells which the analysis discloses 
has no scientific meaning, beyond the statement of the histogenic 
fact. 
Further, it is shown that the tapetum is not a morphological 
constant, but varies both in occurrence and origin; that even the 
individuality of the sporangium is not always maintained. All that 
remains then as the fundamental conception of the sporangium in 
vascular plants is the spore-mother-cell, or cells, and the tissue which 
covers them in, for such cells are always produced internally. The 
definition of the sporangium may then be given thus : ‘ Wherever we 
find in vascular plants a single spore-mother-cell, or connected group 
of them, or their products, this with its protective tissues constitutes 
the essential of an individual sporangium/ From the point of view 
of a theory of sterilization such sporangia may, at least in the simplest 
cases, be regarded as islands of fertile tissue which have retained 
their spore-producing character, while the surrounding tissues have 
been diverted to other uses. It will be seen later how far this view 
will have to be modified in the more complex cases. 
In a second section of the Memoir the variations in number of 
sporangia in vascular plants are discussed ; the methods of variation 
may be tabulated as follows, under the heads of progressive increase 
and decrease : — 
I. Increase in Number of Sporangia . 
(a) By septation, with or without rounding off of the individual 
sporangia. 
(b) By formation of new sporangia, or of new spore-bearing organs, 
which may be in addition to, or interpolated between those 
typically present. 
( c ) By continued apical, or intercalary growth of the parts bearing 
the sporangia. 
(d) By branching of the parts bearing the sporangia. 
(e) Indirectly, by branchings in the non-sporangial region resulting 
in an increased number of sporangial shoots ; this is closely 
related to ( c ) and (d). 
