Apr., 1921] WIELAND — MONOCARPY IN THE CYCADEOIDS 
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A General Conclusion 
On venturing beyond the simpler comparisons with nearly related fossil 
types, it becomes difficult to discuss such a highly specialized and xero- 
phyllous plant as Cycadeoidea. There is the immense pith, the persistent 
armor, and the cauliflorous habit, or production of fruits along the stem 
below the foliage crown. The great thickness of cortical parenchyma in 
some forms need not be mentioned, since in some of the types with a quite 
heavy woody cylinder, as heavy at least as in the Cordaiteans, the pith is 
somewhat reduced, the cortex markedly so. 
But, in the first place, Cycadeoidea in actuality nears certain conifers of 
robust form, and, where branched, finds some resemblance in Araucaria. 
In the tallest cycadeoid trunks, the height may be at least six times the 
stem diameter, exclusive of the armor of leaf bases. Now, in the Chilean 
Araucaria imbricata forest, normally grown old trees may be found with 
a height of only ten or twelve times the diameter of from three to six feet, 
while in the Sequoias of the Mariposa grove a like ratio is found in the case 
of various of the larger trees. For the cypress, taking the gigantic Taxodium 
mucronatum of southern Mexico, the ratio is little if any higher than in 
Cycadeoidea, in contrast to fifty or sixty in the taller conifers. 
Secondly, the wood of Cycadeoidea is of a generalized type which would 
permit innumerable derivatives. The comparative study of tracheids 
suggests this, and it must be true if the complex wood ray structures 
of gymnosperms and angiosperms are mainly of Mesozoic origin, as the 
paleontologic record appears to indicate. 
Thirdly, there is again full sanction in the Mesozoic record for hypothe- 
sizing progressive pith reduction all through that age, not merely in cyca- 
deoids, but in gymnosperms generally. And with pith reduction, branching 
would set in, with great floral and reproductive, as well as foliar, change; 
though here a reverse process may also be conceived, dependent on habitat 
as tropic or high northern. 
Fourthly, the cycadeoid floral type permitted all the sex variation possible 
in any flowers. The angiosperms can vary no more. 
Fifthly, monocarpy which is subject to certain variations in existing 
plants is, in a modified, possibly in a true form, present in the cycadeoids. 
Great lateral series of young fruits, as well as old peduncles seen in four 
species afford the main evidence. 
Sixthly, the cycadeoids of the silicified series are so strikingly xerophyl- 
lous that they go far to indicate vast dry to even cool belts in the mid- 
temperate to northern temperate zone in both Europe and America. The 
organization and protective features are such that light snows and some 
degrees of frost could have been withstood. 
Seeing, therefore, that there can have been such vast change and varia- 
tion in the more generalized cycadeoids, it becomes evident that there 
