Strobilus in Archegoniate Plants . 347 
the centrally lying tissues : {a) that which, as the sporogonium 
elongates, involves the whole thickness of the sporogonium ; 
( b ) that by which single cells are diverted to a vegetative 
development. 
The result of the first type is seen in most Liverworts and 
Mosses ; as examples of its effect we see the sterile foot of the 
Marchantiaceae and Anthoceroteae, but it is more prominently 
shown in the Jungermannieae ; in the latter there is no 
difference in origin or early stages between the central sterile 
region of the seta and the sporogenous mass of the capsule, and 
thus there seems good reason for holding that the former is the 
result of sterile development of a tissue which was in an earlier 
ancestry sporogenous. A similar view will apply with more 
or less clearness to other Bryophyta with stalked capsules. 
Turning to the second type ( b ) of sterilization, in which 
single cells are diverted from the sporogenous to the sterile 
condition, though they are in origin the equivalents of those 
which remain fertile, we shall see that this is widely spread 
through the Archegoniatae, and upwards to the flowering 
plants. Among the Liverworts, Oxymitra , Corsinia. , and 
Boschia show certain cells of the sporogenous mass which, 
though similar in origin, differ at an early stage from those 
which form spores : these commonly take the form of elaters, 
as in Marchantia and Targionia , &c., and are often distributed 
uniformly through the sporogenous mass. 
A peculiar case is that of Frullania , in which the sterile 
cells appear as elongated trabeculae arranged with some 
regularity, and reminding one, as regards their position and 
attachment, of the trabeculae in the large sporangia of Isoetes. 
In other Liverworts these elaters are liable to be grouped 
together, and thus form continuous tissue-masses. This is 
seen to a certain extent in Pellia , where they form a columella- 
like body rising from the base of the capsule ; but better in 
Metzger ia and Aneurct , where the mass hangs down from the 
apex of the sporogonium. These would appear to be im- 
perfect steps towards the formation of a columella in the 
centre of the capsule, by the grouping together of sterile cells, 
