Studies in the Phytogeny of the Filicales. 
VI. Ferns showing the ‘ Acrostichoid ’ Condition, with Special 
Reference to Dipterid Derivatives. 
BY 
/<-• 
F. O. BOWER, Sc.D., F.R.S. 
Regius Professor of B of any in the University of Glasgow, 
With Plates I and II and fifteen Figures in the Te: 
/ «.' v ‘'V.' ■ 
lPR 2 3 ij]>- 1 
“onuj 
T HE old comprehensive genus, Acrostichum, was based upon the fact of 
the exposed sporangia being spread uniformly over a considerable area 
of the sporophyll, and not grouped in distinct sori. It will not be necessary 
here to enter into the history of this genus, or the group of genera, based on 
this feature, nor to trace their various treatment by different authors : since 
this has been recently done by Frau Eva Schumann, in ‘ Flora k 1 Certain of 
the earlier writers appear to have taken this single character alone into 
account in their grouping, with the result that a large number of Ferns 
of very various types were associated together. An extreme position was 
taken up in the ‘ Synopsis Filicum ’, where, as in some other systematic works, 
the genus Acrostichum was made very comprehensive. A natural conse- 
quence was that the genus had to be segregated into numerous sub-genera 
according to their secondary features. But since the time of publication of 
the ‘ Synopsis Filicum ’ evidence has been steadily accumulating, which shows 
that the divergence in the features, then held as secondary, is so great as to 
make it improbable that there is any near relationship of the plants which 
bear them. The question is freely canvassed now, whether the non-soral 
character itself has not been acquired along a number of phyletic lines. In 
fact, it is becoming evident that the c Acrostichoid * condition is not in itself 
a sign of affinity at all ; but a state or condition, which may have been 
attained by Ferns of quite distinct evolutionary history. If this be accepted, 
then Acrostichum is not really a genus of common descent, nor even a 
natural group. But it expresses merely that condition or state of soral 
development in which freely exposed sporangia spring from a considerable 
area of leaf-surface. 
1 I 9 1 5 ? PP- 201-7. 
[Annals of Botany, Vol. XXXI. No. CXXI. January, 1917.] 
B 
