POLYGOKACBOUS GENERA. 33 



others roughened with minute short strigose hairs, the midvein 

 beneath glabrous in the lower, appressed-muricate-roughened 

 in the upper : upper part of stem and the peduncles glandular- 

 scabrous ; spikes 2 or 3 inches long, stout ; bracts muricate- 

 scabrous on the back, not ciliate ; achenes polished, chestnut 

 color. 



Crater Lake, near Plagstaffi, Arizona, Aug., 1884, J. G. Lem- 

 mon. Probably an aquatic of shallow water, becoming ripa- 

 rian. This is a mountaineer of northern Arizona; but more 

 southerly stations, in the heated and half -desert regions yield 

 other species, of terrestrial habitat, which probably do not con- 

 nect with this. 



A diligent study of much material from almost all parts of 

 the United States, occurring in the herbaria under the name of 

 Polygonum Muhlenbergii, more recently denominated P. emersum, 

 has shown that this also is an aggregate of species, some of 

 them strongly marked, others less so. They diifer one from 

 another markedly as to leaf outline and also as to the attitude 

 of the foliage, the leaves in some spreading away from the 

 stem almost divaricately, but in the greater number being ascend- 

 ing or suberect. As to the pubescence, they exhibit not only 

 different degrees but different kinds of hairiness ; and that of 

 the midvein beneath invariably differs from that of the super- 

 ficies of the leaf. In both the form and the indument of the 

 bracts of the spikes one finds also another set of specific char- 

 acters. 



There are also several instances known to me by personal 

 observation in which these species, normally of the land, do 

 under conditions of accidental submersion of the stem, develop 

 floating leaves, and those different not only from those of the 

 terrestrial state, but also very different in general from those of 

 species normally aquatic. Future observation will probably add 

 much to our knowledge of such dimorphic eccentricities in the 

 genus. 



Leaflets, Vol. i, pp. 33-48, March 12, 1904. 



