EFFECT OF ALTITUDE 163 



carried by the wind from the staminate catkins of another 

 branch. After fertilisation these catkins become conelike, and 

 the bracts of the pistillate flowers are then developed into organs 

 of dispersion, which in October scatter the fruits far and wide. 

 Modern artists, in particular Leader and Whistler, have made the 

 birch familiar even to those who seldom get into the country. 



The Scots pine is one of our three native conifers. It is a 

 tree belonging to the post-glacial peat swamps, and it is believed 

 that the Black Wood of Rannoch on the south shores of Loch 

 Rannoch is a part of primitive Caledonian forest. Existing 

 pine woods have as a rule been planted ; for although the pine 

 does produce seed readily, and although seedlings are very 

 numerous, they are constantly eaten down by sheep, rabbits, or 

 deer, and it is only when growing in isolated places, such as on 

 islands in mountain tarns or rivers, that they escape destruction. 

 Pine woods are commonly found near heather moors, and that 

 there is some relationship between the heather moor and the pine 

 is now generally admitted ; it is never found in association with 

 Cotton-grass moors. When the pine has favourable soil it 

 develops a tap-root which penetrates to considerable depth, but 

 in shallow soil the tap-root is not developed. The needle-like 

 leaves remain on the tree for several years, and are always found 

 in pairs. Both staminate and pistillate flowers occur on the 

 same tree, but each set respectively occurs on different branches. 

 The staminate inflorescence is formed at the base of the present 

 year's shoot, and consists of numerous flowers, arranged in the 

 form of a cone. Each staminate flower has numerous stamens 

 which form quantities of pollen, for the tree is wind-pollinated. 

 In the month of June, three distinct sets of pistillate cones will be 

 found on the same tree : small reddish ones at the apex of the 

 shoot of the current year, green succulent ones near the end of 

 the shoot of the preceding year, and brown woody ones near the 

 end of the two-year-old shoot. Each cone consists of scales 

 arranged spirally on a short thick axis, the ovules being borne at 

 the base of the scales. In the young red cones the scales are not 

 tightly pressed together, in order to allow of the pollen falling on 

 to the ovule. On the other hand, the scales of the green cones 

 are very tightly pressed together in order to protect the ovule, for 



