G. R. WI ELAND 
cycadeoid microsporophyll. In fact, if the latter is reduced, as it may be, 
and then imagined to be spirally inserted as in forms already hypothesized, 
the main features of the araucarian staminate cone appear to view. Finally, 
the presence of a leaf gap opposite the outgoing foliar trace in the stem 
and seedling adds still more weight to this far-reaching comparison. The 
double and multiple traces do not of course compare directly with the single 
trace of the known cycadeoids, but with cordaiteans or cycadeans. But 
some or all of the resemblances or parallelisms pointed out must have been 
more marked in the Jura. The araucarians have probably simplified more 
or less since then, in accord with their simple foliage type and narrowing 
distribution. 
Pines, and Gymnosperm Stem Structure 
Amongst gymnosperms the pines of today are of course the type remotest 
from the cyadeoids; but so far as may be judged from the lax or less 
compacted, even leafy, types of gymnosperm cones which prevail in the late 
Paleozoic and early Mesozoic, there may be hypothesized a marked similar- 
ity between some of the ancestral pines and the cycadeoids. This general 
subject is a most difficult one, and adequate study of the abundant gymno- 
sperm stems in most fresh-water deposits of the globe from the Paleozoic 
down has never been made. Obviously such work can be pursued only by 
the most expert students of wood structure. Enough has been done, how- 
ever, to lead to the belief that tracheidal change has followed some fixed 
trend, just as has floral change. 
Bailey and Tupper have examined the size variation in tracheary 
elements of the secondary wood of vascular cryptogams, gymnosperms, and 
angiosperms. It is positive that there has been much decrease in tracheidal 
lengths since the evolution of the upper Devonian Cordaite forest, and in 
widely separated groups. Also, Willis and DeVries have observed a" tend- 
ency of plants to present certain features and groupings or segregations, 
which persist or fail over wide areas. There is a tendency to division into 
"locals" and "wides" which leads to a belief in some ratio of age to area. 
The theory alone is in a sense self-destructive. If changes in secondary 
wood are progressive through the ages, and if in the more superficial char- 
acters of leaf and flower the vegetation of forest and plain is still subject to 
simultaneous change, there is no such thing as age and area. One form is 
about as old as another. But right or wrong, the contributions cited taken 
in combination with the work of Clements on "plant succession," form the 
chief current contribution by botanists to the broader study of evolutionary 
theory.^ 
3 Digressing a bit: Such coordinated change went on amongst the wonderfully pat- 
terned ammonites all over the globe all through the Jurassic. And why not? R. A. Harper 
says: " From the one-celled alga or fungus to the highest plant or animal, the differentiation 
of nucleus, cytoplasm, chromosomes, spindle fibers, etc., is everywhere present; and in 
their general nature and functions and in their interrelations, these structures are the same. 
