158 SCOTCH PINE. 



c. Draw a few cells. 



Place an entire male flower, from whose pollen sacs the 

 pollen has all escaped, between pieces of pith and cut trans- 

 verse sections of the cluster. Chance sections of the walls 

 of the pollen sac will thus be obtained. Examine with 

 a high power, and note 



d. The number of cells in thickness. 



e. The reticulated thickening of the lateral walls, 

 which gives rise to the beaded appearance seen in 

 the surface view. Draw. 



Break open two or three pollen sacs and mount the 

 pollen. Examine with a high power, and note in each 

 grain 



/. The three lobes into which it seems to be divided : 

 a central one, the essential part of the grain ; 

 attached to this two vesicular protrusions or wings 

 with wrinkled surfaces. 

 g. In the central lobe make out 



i. The double wall of the cell ; the outer part, 

 the extine, rather thick and having its 

 slightly roughened external portion expanded 

 into the vesicular wings ; the inner, the inline, 

 very thick and transparent. 



ii. The contents (treat with iodine) ; protoplasm, 

 abundant starch, and sometimes one or two 

 clear-looking drops of oil. 



iii. The division into two cells : one very large, 

 containing the starch and oil ; the other very 

 small, at the end of the central lobe furthest 

 from the wings, best seen when the grain is 

 lying on its side. 



Treat the iodine-stained pollen grains just examined with 

 75^ sulphuric acid. Press gently on the cover glass with 



