CONE-BEARING TREES 



273 



leaves, short branches arise which bear a few scales below, 

 and numerous spirally-arranged stamens above (4). Each 

 stamen has a very short filament ; and the anther bears 

 two pollen-sacs on the under surface (po). When ripe, 

 they split longitudinally and the pollen-grains escape in 

 immense numbers. Each pollen-grain (5) is provided with 

 two air-bladders which serve as floats, and it may be 

 carried a great distance by the wind. When the pollen is 

 shed, the staminate shoots fall off, 

 and the dwarf shoots at the tip 

 develop their pairs of needles. 



The female cone (2, 6, 9) arises 

 near the end of a branch and in the 

 position of a lateral bud. At first 

 it is about a quarter of an inch long, 

 and appears to be terminal, but later 

 it is seen to be lateral (2). It remains 

 on the tree three years, growing 

 larger each season. The cone con- 

 sists of a central axis on which are 

 scale-leaves, and on the upper surface 

 of each scale-leaf grows a much 

 larger, thick, flat, woody scale, i. e. 



the carpel. On the upper surface of each carpel are two 

 straight ovules (orthotropous) (7), with their micropyles (m) 

 pointing towards the axis. They are not enclosed in an 

 ovary ; there is no style and no stigma ; hence there is 

 no pistil as in typical flowers. 



When ready for pollination the axis elongates, lifting the 

 carpels apart, and between them the pollen-grains pass and 

 are carried directly on to the micropyle of the ovule. 

 Pollination occurs in May of the first year, but fertilization 

 does not take place until June of the second year. When 

 ripe the carpels become woody (9), gape open from above 

 downwards, and allow the seeds to escape, each carrying 



Fig. 183. Seedling 

 Pine. c, cotyledons ; 

 /, first green needle- 

 leaves. 



1296 



