CflcU/elter — Relations of SaXix Missouriensia to S. Cordata. 141 



lance form, shorter petioles and less glaucousness. But to me, 

 it appears quite evident, judging both from a review of the 

 table, and comparison of the first two plates, there exists not 

 a demonstrable line of separation justifying a division into 

 two species. This is not saying there is not a form rather 

 peculiar in Missouri and Nebraska. Such form may present 

 itself in Mr. Bush's district in a purer or less mixed state 

 than here about St. Louis. If such be the fact, it could be 

 ascertained only by making an extensive collection in his 

 Ticinity as I have done in mine. 



If we assume two species then the intermediates would have 

 to be regarded as hybrids, but such line of separation could 

 not be drawn between tree and shrub as already shown ; for 

 the parallelism in most of the characters is almost complete ; 

 and besides, assuming any two forms as types, there would 

 still remain the others as side types not fitting in between. 



Have we the typical form of cordata as originally given at 

 St. Louis? I think we have. Having examined a copy of 

 the original drawing by Muhlenberg besides many herbarium 

 specimens from many parts, at the Missouri Botanical Gar- 

 dens, and a specimen personally collected on the "Potomac 

 Flats," D. C, I come to the above conclusion. Moreover, 

 I think we have here all the forms growing in the Mississippi 

 valley and eastward at least to the Falls of Niagara, but not 

 those of California and Mexico. 



Is it not poe 'ble that in some former age these various 

 fo" ns may have arisen in separate regions as very distinct 

 varieties, but now, having in some unknown way been brought 

 together, present an almost protasan and unresolvable com- 

 plexity ? Or what influence may some other species of salix 

 have exerted in modifying the original or its varieties? Ser- 

 Jcea, for example. This latter willow grows sparingly here, 

 but leaves abundant evidence of its contaminating influence 

 on cordata wherever found. At first I felt myself able to 

 distinguish the hybrids thus produced, but finally had to suc- 

 cumb to the indistinctness of the line of separation. This 

 hybridism is found in tree as well as shrub. The silkiness of 

 the Sericea, in the hybrid is often completely lost ; the differ- 

 ing capsule merges into that of cordata. These two 



