CONIFERAE: THE SCOTS PINE 



309 



and bears distally numerous sporophylls or stamens, eacli with two 

 pollen-sacs on its under side (Fig. 251, B, Q. The pollen-grains arc 

 peculiar in bearing right and left of the grain itself air-containing sacs 

 (wings), which give a low specific gravity to the whole grain, and so 

 aid its transfer by the breeze (Fig. 251,/)). At the time when it is 

 shed, the grain of Pinus contains, in addition to the vestigial remains 



Fig. 251. 



Pinus montana. A longitudinal section of a ripe male flower ( x lo). B, longitu- 

 dinal section of a single stamen ( x 20). C, Transverse section of a stamen { a 27). 

 D, a ripe pollen grain of Pinus sylvestris. The obliterated prothaliial cells are n<U 



shown. ( X 400.) (After Strasburger.) 



of two obliterated cells of the male prothallus, one nucleated cell 

 attached laterally (the generative cell), and a free nucleus (the tube 

 nucleus) enclosed in cytoplasm which fills the rest of the grain. 



The male flower is thus a simple shoot bearing sporangia. The 

 female flower may also be regarded as a simple shoot. It consists of 

 an axis bearing numerous scales that are at first succulent, but finally 

 woody. They are arranged on a complex spiral plan. One of these 

 scales removed from the young pink cone at the stage of pollination 

 shows a double structure. A smaller lobe, sometimes called the 

 bract-scale, bears on its upper surface a larger and thickened lobe, 

 sometimes called the ovuliferous scale (Fig. 252). It seems probable 

 that this is a local upgrowth of tissue from the surface of the former, 



