

„Jf"^_ 



NOTE and COMMENT 



Origin of Coal. — That coal is of vegetable origin, no- 

 body doubts, but there still seems to be some uncertainty as 

 to how it was formed. Until recently it has been assumed 

 that coal was produced in vast swamps by the decay of the 

 vegetation growing there, much as the formation of peat in 

 bogs is going on in our own day. According to Jeffrey, how- 

 ever, this idea must be abandoned, a more minute study of 

 coal having indicated that this mineral has resulted from an 

 accumulation of vegetable material in open water transported 

 thither by currents of wind or water. This idea of coal for- 

 mation is likely to be new to many good botanists. It, how- 

 ever, offers a more satisfactory explanation of the origin of 

 certain coals, such as those known to consist almost entirely of 

 the spores and spore-cases of ancient plants. 



Trees and Climate. — It is an interesting fact that tropi- 

 cal vegetation is typically arborescent. Only about 12% of the 

 species in the Torrid zone are herbs. Some entire plant 

 families, in fact, have no herbaceous species. This is true of 

 the conifers, the birches, walnuts, willows, oaks and related 

 plants. Even in cold regions, these families are represented, 

 if represented at all. by woody forms. But in those families 

 with both woody and herbaceous species, the majority of the 

 wood)- forms are in the tropics and the herbaceous species 

 nearer the poles. This is true of the Compositac, the night- 

 shades (Solanaceae), vervains (Verbenaceae), morning-glories 

 {Convolvulaceac) and many others. The Leguminosae well 



