VOLUME LX NUMBER 2 
PHE 
BOTANICAL GAZETTE 
AUGUST 1915 
THE ORIGIN AND RELATIONSHIPS OF THE 
ARAUCARIANS. 
L. LANCELOT BURLINGAME 
The abietinean theory 
This theory has developed more or less gradually and can best 
be understood by tracing the historical sequence of discovery and 
the ideas of relationship that have grown out of them. 
1. Foremost in time and importance was the discovery that the 
steles of ferns, gymnosperms, and angiosperms are characterized 
by a leaf gap opposite the departing leaf trace. To this group was 
given the name Pteropsida. To the remaining groups of vascular 
plants the name Lycopsida was applied. This conception grew 
out of the investigations of the anatomy of Eguisetum (27), the 
stem of angiosperms (28), and the structure and development of 
the stem in pteridophytes and gymnosperms (29). This: dis- 
tinction between these two great groups has been widely accepted 
by botanists and has formed one of the most fundamental ob- 
jections in the minds of many (16, 53) to the lycopod theory. It 
has been questioned by the adherents of the latter theory (54, 61), 
but only in so far as to deny that a phyllosiphonic siphonostele 
(Araucarineae and possibly other conifers) might have arisen from 
a lycopod ancestry. The contention is that this type of stele is 
merely one of the important milestones along the evolutionary 
highway along which all vascular plants tend to travel. It is con- 
ceived to be in the same category as the heterosporic habit, the 
seed habit, and the tendency to reduce the size of the gametophytes. 
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