£32 THE STORY OF THE PLANTS. 



belongs to a quite different famil}'). The male 

 and female catkins of the alder grow on the same 

 tree; the males consist of numerous clustered 

 flowers, three together under a scale, which never- 

 theless, when we take the trouble to pick them 

 out and examine them with a pocket-lens, are 

 seen to resemble very closely the male flowers of 

 the nettle. Each consists of a four-lobed calyx, 

 with four stamens opposite the sepals. The fe- 

 male flowers have degenerated still further, and 

 consist of little more than a scale and an ovary. 



Other well-known wind-fertilised, catkin-bear- 

 ing trees are the oak, the beech, the birch, and the 

 hornbeam. But the willows, though they bear 

 catkins, and were once no doubt wind-fertilised, 

 have now returned once more to insect-fertilisa- 

 tion, as you can easily convince yourself if you 

 stand under a willow tree in early spring, when 

 you wdll hear all the branches alive with the buzz- 

 ing of bees, both wild and domestic. Neverthe- 

 less, the willow, having once lost its petals, has 

 been unable to develop them again. Still, its 

 catkins are far handsomer and more conspicuous 

 than those of its wind-fertilised cousins, owing to 

 the pretty white scales of the female bunches, and 

 the numerous bright yellow stamens of the males. 

 It is this that causes them to be used for " palm " 

 in churches on Palm Sunday. The male and fe- 

 male catkins grow on different trees, so as to en- 

 sure cross-fertilisation, and the difference between 

 the two forms is greater perhaps than in almost 

 any other plant, the males consisting of two 

 showy stamens behind a winged scale, and the 

 Cemales of a peculiar woolly-looking ovary. 



Even more important is the great wind-fertil- 

 ised group of the grasses, to which belong by far 



