Walter Buechler schrieb:
> Dear PaleoListserv member,
> I am interested in changes of venation patterns in response to changes in 
> environmental parameters (temperature, water availability, elevation etc.). So 
> far I found that several modern species of Salix subg. Protitea (according to 
> Skvortsov an evolutionary “retarded” subgenus) may vary from 
> eucamptodromous to brochidodromous (semicraspedodromous?), and to 
> producing straight intramarginal veins as a function of latitude. As an example, 
> Salix nigra is eucamptodromous in Quebec and northeastern USA, and 
> brochidodromous in Florida, Texas, and Mexico). Because of overall climate 
> cooling since Eocene times one would expect to find more brochidodromous 
> Salix leaves in the fossil record than in modern Salix leaves from similar 
> latitudes. This does, however, not seem to be the case. Has anybody seen S. 
> nigra –like fossil leaves (e.g. S. inquirenda, S. succorensis, S. desatoyana or 
> any other long, narrow-leaved species) with a brochidodromous 
> (semicraspedodromous?) venation or an intramarginal vein? I am attaching an 
> image of a cleared S. nigra leaf (from Mexico) as an example of a 
> brochidodromous (semicraspedodromous?) venation pattern. I would very 
> much appreciate any feedback on this matter.
> Sincerely,
> Walter Buechler  
>
>   
Dear Walter,

Can you tell me where this willow tree was growing? Why is it trying to 
conserve water (intramarginal vein), if it is growing on a riverbank? If 
there is enough water available, evapotranspiration is advantageous as 
it will increase the uptake of nutrients and lead to increased growth.

David K. Ferguson