104 G. R. Wieland — Accelerated Cone Growth in Pin us. 



of Welwitschia arisen ? It is certainly thinkable that an ini- 

 tial period of sporophyll reduction and accelerated branching 

 in some ancient pteridospermons ancestor characterized by 

 large bractlike leaves, could result in a growth of fertile axes 

 in compacted groups more or less analogous to that before us, 

 and that a secondary course of reductions may then have inter- 

 vened and produced the condition we now see. In other 

 words, we imagine that in the dioecious Welwitschia single 

 flowers originally derived from fertile terminal buds of vege- 

 tative form have, following increase in number, undergone 

 extreme reduction and modification into " cones," the ovulate 

 forms of which have lost their microsporophylls. Further- 

 more, if each cone of a group more essentially like that illus- 

 trated were to be reduced so as to produce but a single seed, 

 another interesting type of conoid inflorescence would be out- 

 lined ; though such a form could scarcely be as capable of 

 wide variation as a still more primitive series of spirally 

 inserted multiovulate sporophylls.* 



It is thus of decided interest to have clearly brought home 

 to us by such a simple form of accelerated branching as that 

 of Pinus, the very interesting fact that 'by reason of new 

 emplacements wholly new series of modifications in organs of 

 reproduction may take place. These hypothetical en masse 

 changes following the earlier evolutionary stages of primitive 

 sporophylls pointedly suggest how the endless variety of angio- 

 spermous fructifications can have arisen from plant types not 

 very remote from but still more primitive than the Cycade- 

 oidese ; while contrariwise in races with few ovules to the 

 carpel and little phytologic plasticity like the conifers, such 

 realignments and modifications have in post-Triassic time 

 seldom appeared or become habitual with a resultant displace- 

 ment of the plastic stock by its better equipped descendants. 



[April 25, 1906.] 



* The gyninosperm cone itself, both simple and compound, is throughout 

 derived by branching from a primitive main axis. The sporophylls of both 

 sexes are of coarse all derivatives of pteridospermous fronds ; and dorsal, 

 ventral, or lateral insertion of sporangia is of pur ely secondary import, since 

 resulting in the simplest possible manner during the process of extreme 

 reduction in which all circinnate prehoration was displaced by obscured con- 

 duplicate, or direct forms, with formation of various types of appression 

 faces. Finally, in the Coniferales, sclerotization into regularly interlocking 

 spirally inserted prismoids resulted in the nearly aplastic bracts and 

 carpels, which have changed but little since the Jura. Appositely it is 

 hypothesized that a diminution in the number of primitive sporophylls, fol- 

 lowed only secondarily by spore decrease in- number, would conserve the 

 requirements of carpellary plasticity. 



