of Selaginella Amesiana to the genus Selaginella is the 
absence of microsporangia in the strobilus. However, the 
deficiency in this case is of little importance because the 
gametophyte within the megaspore demonstrates clearly 
the female prothallus which, by all of the concepts of 
comparative morphology, implies the existence of the 
male—either on a part of the strobilus which was not 
preserved or upon a separate strobilus. Selaginella 
A mesiana is undoubtedly heterosporous, and is the ear- 
liest known species of Selaginella. 
Conclusions. 
The new species described in this paper as Selaginella 
Amesiana Darrah is a noteworthy addition to our knowl- 
edge of Carboniferous plants, not so much because it 
extends the geological history of the genus into the Pa- 
leozoic era, but rather because this specimen has the fe- 
male gametophyte preserved with almost unbelievable 
detail. Nuclei, nucleoli, cell-plates and at least two rec- 
ognizable mitotic figures are preserved. 
It is so improbable that this example of preservation 
is unique, that one is fascinated by the possibilities sug- 
gested by its discovery. The occurrence of such delicate 
and elusive protoplasmic structures in a fossil of the car- 
bonized compression type, reveals how inadequate are 
our conceptions of the process of petrifaction. 
Three decades have passed since microtechnique was 
introduced into paleobotany by Nathorst, who utilized 
strong chemical reagents to macerate carbonized com- 
pressions. In more recent years Hamshaw ‘Thomas, 
Walton, Lang and Harris have used improved methods 
in this type of work. Halle has developed a paraffin meth- 
od for serial sectioning macerated carbonizations, and in 
our laboratory there has been developed a serial section 
method by the use of nitrocellulose films. The combined 
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