Archenema, protonema and metanema. 
CONWAY MACMILLAN. 
It is intended in this brief paper to call attention to certain 
gametophytic differentiations and possible homologies which, 
while not by any means everywhere overlooked, have not, 
perhaps, received the proper accentuation in current botan- 
ical thought. At the outset it may be well to attempt to give 
a definition of a gametophyte. As understood by the writer, 
this term does not by any means properly apply to every 
plant structure that produces gametes. The Coeloblastee, 
for example, mature undoubted eggs and sperms, but the 
plant body thus functioning can scarcely be termed a gameto- 
phyte. A gametophyte can be defined only in terms of a 
sporophyte held in contradistinction with it. Therefore it is 
only in that group of plants that I have named the Sporo- 
phyta! that. gametophytic structures may be rightly dis- 
cerned. It is inadmissible to apply the term to any plant 
below the position of Gidogonium (or Ulothrix?). A gameto- 
phyte, then, is a structure derived directly or indirectly 
from a sporophytic spore or its analogue, and itself capa- 
ble of producing, directly or indirectly, a gamete or gametes. 
The alge CEdogonium and Coleochete, ‘‘leafy moss plants,” 
fern prothallia, the endosperm of Araucaria, the polfen tube 
of Burmannia and the embryo-sac nuclei of Narcissus are 
types of gametophytes. The definition, it will be observed, 
takes note both of formation and of function. In the case of 
each a reservation must be made, for gametophytes may arise 
directly by propagative methods, as in the breaking up of a 
moss protonema, or by the activity of certain bodies (the 
homologies of which may be with multiple spores rather than 
with propagative structures), such as the gemmz of Aulacom- 
nium and Lunularia. And on the other hand, through apog- 
amy, as in Todea africana, Pteris cretica and a few other 
ferns, or in some less aberrant manner, the gametophytic 
structure may fail to produce gametes. 
_ Thus defined, the gametophyte may be isolated for study 
in any species where it occurs. It should be noted, perhaps, 
<-eieeentsyateeestlibimaiidee inienpionss etme ——— a 
? Metaspermz of the Minn. Valley 20. 1892. 
