CONIFERAE : THE SCOTS PINE 



309 



and bears clistally numerous sporophylls or stamens, each with two 

 pollen-sacs on its under side (Fig. 251, B, C). The pollen-grains are 

 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, D). 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 10). B, longitu- 

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

 D, a ripe pollen grain of Pinus sylvestris. The obliterated prothallial cells are not 

 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 ovuli/erous scale (Fig. 252). It seems probable 

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



