1919] Hall: Chrysotha})iiius tiauseosus and Its Varieties 161 



of these groups comprises only two species, and since these two species 

 are alreach' well defined in the literature and are not inclined to 

 break up into numerous variants in nature, it is at the present time 

 necessary to consider only the nauseosus group. 



Taking Chrysothatiums nauseosus as comprising all of the forms 

 of the Nauseosi, as indicated in the above key. we find its best dis- 

 tinguishbig character to be the presence of a most remarkable pannose 

 tomentum on the young twigs. It is fully recognized that pubescence 

 characters often furnish but a very treacherous basis for constant 

 species, yet in this instance the nature of the -pubescence is so unlike 

 that in any other species of the genus, and it is so obviously correlated 

 with habit and other minor characters that it seems certainly to indi- 

 cate a natural group. This felt-like covering to the twigs is more or 

 less infiltrated with a resinous substance. In some forms the surface 

 is loose and fluffy, the tomentum thus more or less completely masking 

 the striae of the stems. In these forms the surface is usually light 

 gray or dull white or even almost pure white, and the loose tomentum 

 extends even to the involucres. The original C. )iauseosus is one of 

 these forms. In other varieties the surface of the tomentum is firm 

 and smooth, thus revealing the striae. In these forms the twigs are 

 dull to bright yellowish green in color or rarely somewhat whitish 

 and the involucres are mostly glabrous. 



Within what is here included under C. nauseosus, previous writers 

 have described forty forms, all but six of which have been accorded 

 specific rank at one time or another. In the present paper two new 

 varieties are added. Nothing can be more certain than that these 

 forty-two attempts to recognize species and varieties do not by any 

 means exhaust the resources of the group. Everj'- autumnal excursion 

 into a new district brings to light one or more forms not previously 

 described. The only limits set to the number of new species or 

 varieties whicli might be set up lie in one's ability to visit all parts 

 of the field during the flowering period and the failure or disin- 

 clination to recognize minute variations. Yet the systematist should 

 include in his ultimate object not only the recognition of this multi- 

 tude of forms but also their proper arrangement in a scheme which 

 will display their natural relationships. Since this would entail an 

 enormous amount of detailed labor, including extensive experiments, 

 and since the results, even if attainable, would be of but little practical 

 value at the present time, the writer has satisfied himself with the 

 acceptance of twenty-two forms, all of which are treated as varieties. 



