352 Bower . — A Theory of the 
septation among Angiosperms is but sporadic : that it is 
merely an ‘adaptive’ character, and that the sporadic 
occurrence of it deprives it of systematic importance. In 
answer to such objections I would say that to me all per- 
manent morphological characters are probably at one time or 
another ‘ adaptive,’ though we may distinguish between those 
which are results of relatively recent adaptation and those 
which were relatively primitive. It may be that the same 
method of advance may have brought in its train important 
physiological advantages at one point of evolutionary history : 
but when repeated at a later period the advantages may have 
been less weighty : the result would be in the one case relative 
permanence, in the other less permanence. This I conceive 
to be the case for septation of sporangia in the homosporous 
Archegoniatae as compared with septation of anthers in 
Angiospermic plants. 
But while we thus recognize that parts of the sporogenous 
tissue may form sterile septa, I have been able to show that 
the converse may also take place ; viz. that tissue of a septum, 
which is normally sterile, may on occasions form spores. 
This occurs in certain abnormal synangia of Tmesipteris , and 
is, in my view, a reversion. In Fig. 161 of my memoir in the 
Philosophical Transactions 1 , a synangium of almost normal 
form is seen : but though the position of the usual septum is 
clearly indicated, the cells there are already assuming the 
character of tapetum or of sporogenous cells, as is more 
clearly seen in Fig. 162, where they are represented in a draw- 
ing on a larger scale. This conversion of the sterile septum 
into sporogenous tissue is more conclusively shown in Fig. 164, 
in which the development is slightly more advanced, while 
Fig. 165 represents a part of the contents about the line ( x ) 
where the septum should normally be : here it is seen that 
sporogenous cells form a continuous chain across the line, thus 
conclusively proving that the normally sterile septum has 
become sporogenous. 
The conclusion to be drawn from such observations, together 
1 See Proc. Roy. Soc., No. 326, 1893. 
