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1894. ] Archenema, Protonema and Metanema. 23 
Three structural categories of gametophytes have now been 
established in this discussion; archenema, protonema and 
metanema. The very important question then arises:—what 
are the homologies of the fern. prothallium? It is apparent 
that there is no @ priori reason why it may not be any one of 
the three. In Coleochete the gametangia are borne upon 
archenema; in Buxbaumia at least the antheridia are produced 
upon protonema (Goebel), while in the great majority of 
Hepatice and Musci the gametangia are altogether metane- 
mal in their origin. The fern prothallium might then be 
considered as a developed Coleochete-like structure which 
has not passed through the differentiation into protonema and 
metanema; or it may be regarded as a thalloid protonema, 
the metanemal companion stage of which has been suppressed 
by reduction; or again as a metanema, the embryonal pro- 
tonemal stage of which has disappeared. It will be seen at 
once that the correct interpretation of the facts in the case is 
of great importance. Especially, in view of the fact that 
there is a modern effort to reach the conclusions of fern phyl- 
ogeny from the gametophytic as well as from the sporophytic 
side of the organism, is it imperative that the three possibili- 
ties be held distinctly in view. Indeed it would seem as if 
the criticism here undertaken might indicate the necessity for 
a revision of some important conclusions which have been 
put forth recently by students of the Archegoniate. For 
example, I am here strongly inclined to criticise the position 
maintained by Campbell® that ‘‘the prothallium of Hymeno- 
phyllum corresponds not merely to the protonema of a moss, 
but to the protonema f/us the leafy plant.” It is not that 
the position may not be a sound one (for the prothallium may 
indeed be archenema), but because the verdict should as yet be 
the Scotch verdict. And especially, in view of the very able 
and convincing argument of Campbell in favor of considering 
the eusporangiate ferns as basal and derived from the vicinity 
of Anthoceros with its undoubted metanema, must one hesi- 
tate to regard the prothallium of Hymenophyllum or any 
other fern as archenemal. But if not archenemal it must ap- 
parently correspond with either protonema or metanema. 
There is of course the possibility of arguing the derivation of 
the fern prothallium from archenéina, and its independent dif- 
ferentiation into protonemal and metanemal stages. The 
*Campbell, On the affinities of the Filicinex. Bot. Gaz. 15: 1. 1890. 
