THE GENERA OF MOSSES. 
119 
had emerged from the perichastial leaves, that we clearly 
ascertained it to possess one occupying a large proportion 
of the theca, and bearing on its summit the opercular mem 
brane. The appearance it generally assumes in maturity is 
that of a convex membrane lying across the bottom of the 
theca, suggesting the idea, that a lining to the base had se- 
parated from its attachment, and had been somewhat elevat- 
ed without laceration. 
We have dwelt perhaps rather longer on the columella 
than we ourselves originally intended. Our excuse must be, 
that we really consider it to be an important organ, the 
economy of which is at present involved in obscurity ; and 
we cannot regard it in the same point of view as Mr Brown 
and Dr Hooker seem to do, however unwilling we may be 
to differ from two of the most learned authorities of the 
present day. 
Dr Hooker * conceives the columella to be " nothing 
more than the remains of the cellular and pulpy substance 
in which the seeds have not been perfected, and which, as 
we may consequently expect, shrinks up into an angular 
axis or columella." In this passage, as in the following, 
we conceive the columella to be spoken of generally. 
" In some cases," says Mr Brown ^f, " the seeds may be 
formed in a much greater portion of the columella than in 
others ; and it is even not improbable that, in certain cases, 
its whole substance may be converted into seeds ; or, to 
speak more accurately, that it may produce seeds even to 
the centre, and that the cells in which they were probably 
formed may be reabsorbed." 
The late Professor Richard was also of the same opi- 
* Flora Londinensis, New Series, under Dipliyscivm folimum, 
I Linn. Trans, vol. x. p. 312, 
