Tee. 
VOLUME XLVIII ‘NUMBER 2 
BOTANICAL GAZEPTe 
AUGUST 7909 
EVOLUTIONARY TENDENCIES AMONG 
GYMNOSPERMS 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 127 
JoHN M. COULTER 
The investigation of gymnosperms has proceeded with such vigor 
that some adequate picture of the group freed from its details may 
now be obtained. The confusion of details often obscures the impor- 
tant facts, and it may be of service, at this stage of our knowledge, to 
emphasize them. There is no better way in which to develop a 
clear picture of a great group than to select those facts of structure 
that enter into its general evolutionary history. This has nothing to 
do with differences among species, or even among genera, which may 
be left to the taxonomist; but it deals with those general tendencies 
to change structures which can be noted in passing from the most 
ancient gymnosperms to the most recent. ; 
While the discovery of these tendencies aids in reaching conclusions 
_ in reference to the phylogenetic connections of the groups of gymno- 
sperms, it must be remembered that the tendencies are facts and the 
phylogenetic conclusions are very uncertain inferences. Moreover, 
_ a general tendency expresses itself throughout a great group, and has 
_ to do with the transition from ancient to modern forms, rather than 
_ with the breaking-up of the group into several phylogenetic lines. 
_ Failure to remember this fact has been responsible for much sterile 
_ inference as to relationships, similar stages in some general tendency 
_ being assumed to mean immediate genetic connection. The organ- 
_ ism is a plexus of structures, and must be considered in its totality 
_ when relationships are being considered. Among the general tend- 
_ encies leading to the origin of seed plants, for example, that which 
_ Tesulted in heterospory must be regarded as of paramount importance, 
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