I IO 
Lillian O'Keeffe. 
which implies phylogenetic reduction from a type like Marchantia, 
while as we have seen every transition may be found in Targionia 
between condensed male shoots of limited growth and well-developed 
ordinary thalli bearing antheridia. 
IV. Archegonial Receptacle. 
The development of the archegonial receptacle and of the 
involucre has been described by Leitgeb (9), Campbell (2) and 
Deutsch (6), the last writer introducing the useful term “ fruiting 
surface” for the surface or pad on which the archegonia are borne 
terminally on the thallus. This surface, on which the archegonia, 
usually about 7 but up to 9 or 10 in number in some cases, are 
developed in acropetal order in a zigzag row, slopes forward and 
downward; the apical cell is clearly seen in front of the youngest 
archegonium, and since each of its dorsal segments produces an 
archegonium, these organs are at first closely crowded, very little 
vegetative tissue being formed in the upper part of the thallus in 
this region. The result is that the archegonial surface comes to lie 
in a shallow depression, the lower (anterior) margin of which is 
occupied by the apical cell—the time at which this cell ceases to 
function appears to be, like the number of archegonia produced, 
conditioned by the occurrence of fertilisation in one or more of the 
archegonia. As Deutsch points out, the development of the involucre 
is closely bound up with that of the archegonial or fruiting surface, 
and it may in fact be considered as simply representing the lateral 
or peripheral region of this surface, the earliest stages in its 
development synchronising with the appearance of the first arche¬ 
gonia, and consisting simply in the forward growth of the tissue 
around the archegonial depression to form two curved lateral ridges. 
These ridges at first consist of compact tissue, but at a later stage 
air-chambers are developed, especially in the upper portion of each 
ridge, so that when mature the involucre, the two valves of which 
have been formed by the continued growth of the ridges, appears 
in vertical transverse sections as a continuation of the ordinary 
thallus tissue, each valve having air-chambers in its upper portion. 
As the valves of the involucre grow forward they curve inwards 
towards the middle line of the archegonial surface, keeping pace 
with the growth in length of the archegonia, and their free edges 
come close together so that the opening to the archegonial depression 
becomes narrowed and slit-like. Deutsch reports a case in which 
the involucre was “complete and well developed while the eggs of 
