294 COMMON TREES AND SHRUBS 



stamens (Fig. 194, 4). The female catkins arise near the end 

 of the twigs and bear only one to five flowers. The stalk 

 of the catkin is long in the Stalked Oak and much shorter 

 in the Sessile Oak. Each flower (5 and 6) arises in the 

 axil of a bract and is surrounded by a shallow cupule. The 

 pistil consists of three united carpels ; the ovary is in- 

 ferior and three-celled (7), with two ovules in each cell, 

 but the ovules are not formed until after pollination. The 

 stigmas are broad, red, and three-lobed. Usually only one 

 ovule develops into a seed, though very small ones may 

 also be found within the polished shell of the acorn. For 

 the structure of the acorn see Fig. 143. 



A comparison of the flowers of such catkin-bearing trees 

 as Hazel, Birch, Alder, Beech, and Oak shows that they 

 differ in several important respects from those of Willows 

 and Poplars. In the Willows and Poplars (Salicaceae) the 

 flowers are dioecious, naked, i. e. they have no perianth, 

 and hypogynous. The pistil consists of two united carpels ; 

 the ovary is one-celled with many ovules ; the fruit is 

 a dehiscent capsule, and the seeds have a tuft of hairs. 

 In the Hazel, Birch, and others, the flowers are monoecious, 

 and have an epigynous perianth. The pistil has two or 

 three united carpels ; the ovary is two-celled with one or 

 two ovules in each cell, and the fruit is an indehiscent, one- 

 seeded nut. 



In each case the flowers are small and inconspicuous. 

 The stamens produce a large quantity of dry pollen carried 

 by the wind to the large branched stigmas of the female 

 flowers. 



