When the seeds in this catkin are ripe they resemble tiny nuts with wings on each side (5): and on windy days you can see clouds of these little winged seeds (5_a_) fluttering to the ground like small flies. Birds are very fond of Birch tree seeds, and one kind of finch, the siskin, is usually found hovering among the Birch trees. The Birch tree lives till it is about a hundred years old. It is not grown up till it is twenty-five, so you will find no seeds on the young birches. It is a tree with many useful qualities. The bark is sometimes twisted into torches, as it contains a good deal of oil, and it is also used in tanning leather. The delicious scent of Russian leather is due to Birch bark oil. And there is sugar in the sap which may be made into wine. Furniture is largely made from the prettily grained Birch wood. PLATE IV THE ALDER The Alder tree (1) is a cousin of the Birch and the Hazel, and like them its flowers and seeds are borne in catkins. It is usually to be found growing by the side of a slow-running stream, over which its slender branches bend gracefully, while its spreading roots cling to the boggy soil at the water’s edge. For the Alder does not thrive in dry ground: it is a water-loving tree, and its many tiny roots attract moisture, and suck it up greedily; so that the ground where the Alder grows is often a marshy swamp. Sometimes you will find an Alder which has grown into a lofty tree with a rough brown-black bark, and with many large branches; but it is much more frequently found as a low-growing and rather gloomy bush, about the same size as the Hazel. The wood of the Alder is much sought after for buildings which stand in water. In Venice one of the most famous bridges, the Rialto, is built on piles, or great posts of Alder driven deep into the bed of the canal: and one reads in old history books that boats were first made of the trunks of the Alder tree. But it is of no use for fences or gate posts, as it decays quickly in dry soil. [Illustration: PLATE IV THE ALDER 1. Alder Tree 2. Leaf Spray 3. Stamen Catkins 4. Seed Catkins 5. Last Year’s Seed Catkins 6. Next Year’s Seed Catkins] If you watch a woodman cutting down an Alder tree you will notice that the chips which fall under his axe are very white; but soon they change colour and become a reddish pink. The hard wood knots which are found in the tree trunk are beautifully streaked and veined and are much prized by furniture makers.