THE BLACK POPLARS. I9 



and all dififering in foliage from the European species as given 

 above. These are distinguishable as follows : — 



1. Populus deltoidea var. inojiilifera^ Henry yPopulus monilifera, 

 Alton, Hort. Kew., iii., 406 (1789)]. 



Leaves deltoid-ovate, about 3 inches long and wide, abruptly 

 contracted into a long non-serrated apex ; base wide and 

 shallowly cordate, bearing two glands at the junction with the 

 petiole in front ; margin densely ciliate ; both surfaces and 

 petiole quite glabrous, except for a few evanescent hairs on the 

 midrib and main nerves. 



This variety, which may be conveniently called P. monilifera, 

 is wild in Ontario, Quebec, New England, New York and 

 Pennsylvania. Its habit is shown by Fig. 4, representing a tree 

 growing near Ithaca (N.Y.), about 100 feet in height and 13 feet 

 in girth at 5 feet above the ground. 



This poplar was introduced early (about 1700) into France 

 and England, but has not been propagated for many years as 

 it was supplanted by the fast-growing hybrids. The only tree 

 that I have seen in England was one in the Cambridge Botanic 

 Garden, cut down some years ago, but replaced by a cutting, 

 which is thriving. There are two other old trees in England 

 which have been identified with this species. No tree is more 

 easy to identify by the form of the leaves ; and it is remarkable 

 that the unlikeness of the hybrid forms escaped notice, the 

 latter still masquerading in books and nursery catalogues as 

 P. monilifera or its synonym P. canadensis, names only applicable 

 to the true American species. 



2. Populus deltoidea var. occidentalis, Rydberg \_Populus 

 Sargentii, Dode (1905); Populus occidentalis, Britton (1906)]. 



Leaves smaller than in the preceding, thicker in texture, and 

 lighter in colour, deltoid, truncate at the base, with fewer and 

 coarser serrations ; glabrous. 



This, which is the xerophytic form of the species, grows in 

 North America in the territory east of the Rocky Mountains, 

 from Saskatchewan and Alberta southwards to New Mexico and 

 western Texas, and is the characteristic tree on the river flats of 

 the western prairies. It has not been introduced. 



3. Populus deltoidea var. missouriensis, Henry [P, angulata 

 var. missouriensis, Henry, in Trees of Great Britain, vii., 181 1 



<i9i3)]- 



Leaves similar in shape to those of var. monilifera, but larger, 



