Davis . — The Origin of the Archegonium . 479 
matter, but it becomes of utmost importance when it rests 
on a clear morphological basis. It seems to the writer that 
the peculiarities of the reproductive organs of most Thallo- 
phytes justify a most careful consideration of the above 
suggestions, and he will employ the terminology throughout 
this paper as the best means of making clear the fundamental 
distinctions between the archegonium and antheridium of the 
Bryophytes and the reproductive organs of most Algae. 
There are of course no archegonia in the Thallophytes, and 
antheridia in the narrower use of the expression (i. e. multi- 
cellular organs) are only represented by such structures as are 
found in the Characeae, and less conspicuously in groups of 
sperm-producing cells occasionally found among the green and 
brown Algae (e. g. Oedogonium , Dictyota). 
Logically, the term 4 antheridium ’ should be strictly reserved 
for such multicellular structures as have clearly developed from 
a single cell whose activities produce tissues with a definite 
form and function. The antheridium of Chara is such an 
example, and the antheridia of all plants above the Thallo- 
phytes illustrate clearly the point. On the contrary, many 
so-called antheridia of Algae, especially among the Rhodo- 
phyceae, are simply groups of antherocysts, independent cells 
that happen to be associated together but are not tissues. 
The antheridia of Bryophytes present clearly the distinctions 
between the antherocyst, a single cell, and the tissue with 
definite form whose co-operating cells establish an organ. 
The method of development of the antheridium is the basis 
of these fundamental distinctions. A superficial cell generally 
begins the process by several oblique divisions, which frequently 
result in the differentiation of a terminal cell that plays an im- 
portant part in defining the form of the structure. This apical 
cell, if present, cuts off segments that build up the antheridium 
from above. If there is no clearly differentiated apical cell, 
the structure increases in size by various cell-divisions in its 
mass. Finally, periclinal walls separate a sterile layer of cells 
on the exterior from a central group. The latter divide by 
walls at right angles to one another into small cubical cells, 
