90 Rhodora [Marcu 
A NEW BIDENS FROM THE MERRIMAC VALLEY. 
M. L. FERNALD. 
' (Plate 45, figures 11-20.) 
IN September, 1902, Mr. Alvah A. Eaton sent to the Gray Herba- 
rium a Bidens which for some years he had vainly attempted to recon- 
cile with descriptions. Mr. Eaton's plant occurred on brackish shores 
of the Merrimac River above Newburyport, and, though in habit and 
in the shape of its heads it strongly suggested Bidens bidentoides of 
the lower Delaware River, its shorter heads and achenes and shorter 
stouter awns prevented its identification with that local species. 
The plant was so unlike any Bidens known to the writer, that 
arrangements were made with its discoverer for a visit to the station 
on October second. But since the tide at mid-day was so high that 
the back-flow of the river covered the brackish shores above New- 
buryport, the original locality of the plant was inaccessible before late 
afternoon. In the meantime, however, the marshes on the Salisbury 
side of the river were explored. ‘There on the brackish margins of 
streams whose banks are overflowed during high-tide were Bidens cer- 
nua, B. connata and B. frondosa and occasional colonies of the 
strange Bidens previously known from above Newburyport. In foli- 
age the plant somewhat resembled B. connata, but while that species 
as well as B. cernua and the pinnate-leaved B. frondosa invariably had 
broad hemispherical heads, the plant which had led us to the muddy 
shores was readily distinguished by its cylindric or narrowly oblong 
heads. Later in the day, on the muddy shore above Newburyport 
where Mr. Eaton had first detected the plant with cylindric heads, 
it was found maintaining its habital character as it had done by the 
pools in Salisbury. 
A detailed study of the material then collected has shown that the 
plant of the Merrimac shows affinities with Bidens connata, B. com- 
osa and B. bidentoides. 
From Bidens bidentoides the Merrimac plant is distinguished by its 
shorter heads, its much broader achenes and its shorter awns. From 
B. connata and B. comosa as already stated it is readily distinguished 
by its narrow elongate heads, but to both these species it approaches 
in certain other characters. As in B, connata the inner bracts of the 
