FLOWERS AND THEIR WORK. 247 



the axil of a bract. In Willows the male catkins are bright yellow, the 

 female ones green, when the flowers open. Each male flower consists 

 of two (in some species more) stamens, with a honey-gland at their 

 base ; the female flower of a pistil with two stigma-lobes (each often 

 forked at the end), ovary one-chambered with numerous ovules on 

 two parietal placentas, and a honey-gland. The flowers are largely 

 visited by bees seeking for honey and pollen among the scanty spring 

 flowers. 



In Poplars each male flower has a larger number of stamens (twenty 

 to thirty), surrounded at the base by a cup-like outgrowth ( " perianth "), 

 and the female flower of a pistil (similar in structure to that of Willows) 

 with branched stigmas forming a tuft ; in neither case is there a honey- 

 gland. The Poplars are wind-pollinated ; their flowers have no honey 

 to attract insects. More pollen is produced than in Willows, and the 

 stigmas are more branched, exposing a larger surface ; the catkins of 

 Poplars hang down loosely and swing in the wind, and are longer than 

 those of Willows, which usually stand out stiffly from the stem. 

 Moreover, Poplars flower before the leaves appear, and their flowering 

 is generally over by April, when most Willows are beginning to 

 flower ; many Willows flower at the same time that the leaves 

 expand. 



275. Birch., Hazel, Oak, etc. Many forest-trees bear their 

 flowers (or at least the male flowers) in catkins, or in clusters re- 

 sembling catkins, but have the male and female flowers on the same 

 plant. In Birch, Alder, and Hazel the male catkins hang down, so 

 that the stamens are covered by the scales (bracts) to which they are 

 attached (as in Poplar), and thus protected from rain. The female 

 catkins are smaller, with stigmas projecting beyond the scales. In 

 Hazel and Alder the catkins are formed from special buds, and are 

 nearly mature in the autumn, ready to open early in spring, before the 

 leaves. In Birch the female catkins are formed in the ordinary buds, 

 and appear along with the leaves. This is also the case with both male 

 and female flowers in Beech and Oak, in which the male flowers have a 

 cup-like "calyx" ; in Beech the male flowers are in a cluster at the 

 end of a long drooping stalk, in Oak they are scattered along a similar 

 stalk. 



276. Other Wind-Pollinated Flowers. Plants with wind- 

 pollinated flowers occur in some families which are chiefly insect- 

 pollinated e.g. Meadow-rue (Thalictrum) in Ranunculaceae, Salad 

 Burnet (Poterium) in Rosaceae. Compare their flowers with those 

 of allied plants in the same family. Examine also the following 

 flowers : 



Pine, Larch., Yew. In these plants the stamens and carpels are 

 on special branches (cones), the pollen is produced in enormous abun- 

 dance, and the ovules are exposed, so that the pollen-grains reach the 

 micropyle directly. 



