316 BOTANICAL GAZETTE [may 
faces the base of the archegone instead of the neck. If it be 
accepted that the new position of the Angiopteris archegone as 
compared with the position of the same organ in the arche- 
typal Anthoceros is an adaptation for protection it is apparent 
that class A above is easily divided into two subclasses as fol- 
lows: 
A. Primitive orientation. 
1. Archegone in original position, ¢. g., Equisetum. 
2. Archegone in adaptive position, @.%., Angiopteris. 
To interpret the semi-inverted orientation of Pteris from the 
conditions in Angiopteris is possible if we regard it as a further 
adaptive modification. It may be conceived to be of advantage 
to the young embryo to grow through the least resistant tissues 
of the prothallium upon the ventral side of which it had origi- 
nated. Any tipping of the egg so that the epibasal hemisphere 
should incline towards the growing point of the prothallium 
would subserve this end, and at the same time would more 
definitely place the absorptive hypobasal area in the most advan- 
tageous position with reference to the older, nutriment-contai 
ing portion of the gametophyte. Such an adaptive ile 
forward of the epibasal hemisphere would be perpetuated, ow 
at the same time might be accentuated until the change 1" aan 
tion exceeded go° as is the case if one compares bee a 
Angiopteris. The position, then, of the epibasal hemispher - 
the Pteris embryo has an interesting suggestion eee oe 
phylogenetic history of the prothallium. Clearly the alight 
almost unilamellar prothallium of the Polypodiacee offers SiS 
resistance even if an embryo were to penetrate it 
its cotyledon or stem-apex. Therefore it seems ae 
regard the semi-inverted embryo as suggesting ae ue ng for- 
prothallia were much thicker, and that the habit o pier 
ward dates from the time of thick prothallia. This 1s P ‘ 
in accord with many other bits of evidence tne gf te 
toward the same conclusion. And, part pass, . 
embryo in Trichomanes, suggesting as it does its a : 
acter of the filamentous prothallium, renders it di 
; 
a 
' 
] 
: 
directly with 
