TiO BOTANICAL GAZETTE [AUGUST 
Summary 
1. The science of phylogeny possesses fairly adequate and 
reasonably trustworthy rules of evidence. 
2. The degree of relationship is most clearly indicated by a 
detailed and accurate comparison of all the structures of the plant in 
all the stages of development, and is roughly proportional to the 
number and exactness of the resemblances. 
3. Conclusions derived from direct comparisons should be 
checked carefully by the geological record. 
4. Direct comparisons may be supplemented by indirect com- 
parisons instituted through the use of more or less valid conclu- 
sions derived from the presence of supposed vestigial structures in 
primitive regions and from recapitulationary phenomena. Such — 
indirect comparisons afford much less certain conclusions. 
5. Reversions to ancestral conditions may sometimes occur 
under normal conditions or be experimentally produced by wound- 
ing or unusual conditions of growth. Conclusions based on evi- 
dence of this sort have little weight unless supported by other more 
reliable sorts of evidence. 
6. Gymnosperms as a group resemble one another much more 
closely in very many ways than any one of them resembles any other 
group. They are, therefore, monophyletic. Since the cycado- 
phytes are almost certainly derived from a filicinean ancestry, it 
follows that all are ultimately traceable to the same source. 
7. The conifers closely resemble Cordaitales and are probably 
derived from them. 
8. Araucarineae resemble the Cordaitales far more closely than 
do any other conifers, and are probably derived directly from them. 
This conclusion is consistent with the geological record. 
g. The transitional conifers of the Mesozoic are either arau- 
carians or cordaiteans well on their way toward Pinaceae. Some 
of them may be actually ancestral to such Taxodineae as Crypio- 
meria and Sequoia. 
10. The Abietineae are very old and are derived either directly 
from the Cordaitales or from the very ancient members of the 
Araucarineae. 
STANFORD UNIVERSITY 
‘CALIFORNIA 
