TREES AND SHRUBS. 389 



The buds are long, pointed, smooth ; each has four scales an outer 

 concave scale on the side away from the stem and three inner ones. 

 In spring these scales fall off, together with the stipules of the sticky 

 young foliage-leaves. The side buds generally grow into dwarf shoots 

 or into catkins, while the end bud grows into a long shoot. The 

 highest bud is not really the end bud ; as in many other trees, the real 

 end bud does not develop at all, the highest axillary or side bud re- 

 placing it in growth. 



The long hanging catkins open before the leaves unfold. Each 

 catkin is produced from a special bud, which resembles an ordinary 

 bud in having four scales. The bracts are fringed at the free (outer) 

 edge, but are not hairy. Each flower has a short stalk bearing a 

 shallow lop-sided cup-like organ. 



In a male catkin we find within this cup a tuft of stamens (about 

 forty), each with a red anther. At first the male catkin is erect or 

 horizontal and the filaments are very short, but soon the catkin-axis 

 lengthens, the catkin droops, the bracts fall off, and the filaments 

 rapidly grow longer and push out the anthers. Then the anthers 

 open and shed the pollen, which is carried by the wind, and very 

 soon the whole catkin falls off the tree. 



In the female catkin the cup surrounds the base of the pistil ; above 

 the ovary (one -chambered, with numerous ovules in two lines on the 

 wall) are two large yellow branched stigmas. After pollination the 

 axis of the catkin lengthens and the ovary grows into the fruit 

 (capsule), which splits down along two lines halfway between the two 

 lines of seeds, then the two valves roll outwards and the seeds escape. 

 Each seed has a tuft of hairs serving for wind-dispersal. 



For a comparison of the flowers of Poplars and Willows see 

 Art. 274. 



380. The Loxnbardy Poplar is simply a "pyramidal" variety of 

 the Black Poplar, distinguished by its deeply furrowed bark and 

 especially by the strong tendency shown by the branches to bend 

 upwards and grow erect. Connected with this peculiar habit, which 

 enables one to recognise the tree from a great distance, is the fact that 

 only the buds on the outer side of the tree, i.e. those which are most 

 exposed to light, grow out to form shoots. 



381. The Aspen, the smallest of the common Poplars, is rarely 

 over fifty feet high, with a slender trunk (about 1 ft. diameter). The 

 bark remains smooth and light-coloured for many years ; the leaves are 

 rounded and not pointed. The buds and flowers resemble those of 

 Black Poplar, but the flowering buds are more distinct from the 

 ordinary buds, being larger and less pointed ; the bracts bear numerous 

 long hairs on their edges ; the stamens are fewer (about ten) ; the 

 stigmas are red, not yellow. 



382. The White Poplar resembles the Aspen in many respects, 

 but is easily distinguished by (1) the white down on its leaves (lower 

 side) and young twigs, (2) the dry and hairy buds, (3) the frequently 



