BLACK POPLAR. 631 



MATURE LEAVES. 



The form of the leaves is subject to great variation, not only 

 between the species and between the individual trees of a species, 

 but in the foliage of a single tree. Those of the Aspen most 

 nearly approach a circle, with large widely-spaced teeth, and have 

 the longest and the most flattened footstalks. The leaf of the Grey 

 Poplar resembles them in form, but the outline is less regular, and 

 the leaves springing from the suckers are cut up by two pointed 

 lobes, which give them a likeness to those of the White Poplar. The 

 leaves of the Black Poplar vary from heart-shaped to triangular. On 

 the Lombardy Poplar they are smaller; on the Balsam Poplar, which 

 has the least flexible foot-stalk of any variety, they are larger and 

 inclining to egg-shaped. Both surfaces of the leaf-blade in the Black 

 Poplar and its varieties are smooth and remarkably alike. The White 

 Poplar is distinguished by a dense white wool covering its under- 

 side, the Grey by one less dense which is lost before the autumn. 

 Both surfaces of the Aspen are usually smooth : sometimes the under 

 surface is silky ; the upper surface is either glossy or dull. 



THE CATKINS. 



The Catkins agree in having hairy bracts which sub-tend the 

 scales. The stamens of the male flowers vary in number ; the Aspen 

 and White Poplar have from four to ten, the Balsam from twenty 

 to thirty, the Black and the Lombardy from twelve to twenty. The 

 female catkins of the White Poplar carry two stigmas with divided 

 tips. The Black Poplar has four stigmas, the Grey four also, with their 

 tips sub-divided into Jour. There appear to be no female catkins on 

 the Lombardy Poplars, as only male trees were imported. The stigmas 

 of the Aspen are branched at their tips. Differences also appear in 

 the scales of the catkins : on the Aspen they are lobed and notched, 

 on tin- White Poplar notched, on the Grey deeply cut. 



