164 SCOTCH PIN. 



As soon as the male flowers begin to scatter their 

 pollen to the wind, the axis of the young cones elon- 

 gates, separating the carpellary scales sufficiently 

 to allow the pollen to be blown in between them, 

 and to slide down, guided by the keel, to the pro- 

 longations of the integument. These prolongations 

 subsequently roll inward, thus carrying any grains 

 which may have become attached to them to the apex 

 of the nucellus. After this process of pollination is 

 accomplished the bracts cease to develop and like- 

 wise the now useless keel. 19 



The minute anatomy of the Scotch pine presents 

 many points of considerable interest. 



True tracheary tissue is formed only at the peri- 

 phery of the pith, where a cluster of spiral, reticulated 

 and pitted vessels occurs at the apex of each woody 

 wedge. 



The tissue of the wood is almost exclusively made 

 up of tracheides, on whose radial walls are bordered 

 pits. As these walls, originally thin and plain, increase 

 in thickness irregularly, a part of the thickening on 

 each side of the primary wall grows away from it 

 to form the arched " border " of the small aperture 

 which remains. For some time the primary wall 

 remains as a membrane separating the two cells ; 

 when finally this is destroyed there is free communica- 

 tion between the contiguous cells. 20 



The thin delicate walls of the cambium allow great 

 activity of the contained protoplasm, which results 



19 Strasburger, op. cit., p. 476. 



20 Cf. Strasburger, Bau und Wachsthum der Zellhaute, p. 43, taf. 

 iii. For figures cf. Sachs, Text-book, p. 25. 



