EXERCISE 102 

 REPRODUCTION OF THE PINE 



Materials. Cones of the season containing seeds, one-year-old 

 cones on branches, and branches with young staminate and pistillate 

 cones ; pinon seeds. 



Directions for work. The familiar pine tree is the sporophyte 

 generation, bearing two kinds of asexual spores, one of which 

 is illustrated by the pollen grains. The gametophyte generation 

 is so reduced that it can be studied only by the aid of the 

 compound microscope. The gametophytes will not be included 

 in the laboratory work. 



1. Staminate cones. The cones are composed of a central axis 

 bearing overlapping leaves. Split a cone through the center to 

 see the attachment of the scales to the axis. Pick off one of 

 these scales, or stamens, and find the two pollen sacs (sporangia) 

 on the under surface. Make a diagram to show the arrangement 

 of the scales on the stem and another to show the form of the 

 stamen and its pollen sacs. 



Break open one of the pollen sacs and mount the pollen for 

 observation with the microscope. Note the two wings which 

 assist in distribution by the air. 



The pine is wind-pollinated. Is this an economical method 

 so far as amount of pollen required is concerned ? Place a 

 cluster of fresh cones which have riot shed their pollen in a cup 

 and allow them to remain for several days. Note the quantity 

 of pollen collected. 



2. Young pistillate cones. Note the arrangement of the scales. 

 Remove several and find the two ovules on the base of each. 

 Make a diagram showing the arrangement of the scales on the 

 axis and the position of the ovules on the scales. 



Are these ovules inclosed in an ovary as are those of flowering 

 plants? Can the pollen grains which the wind deposits on these 

 cones come into actual contact with the ovules, or is there a 

 style, stigma, etc., as in flowering plants? 



3. One-year-old cones. Examine scales from these to see the 

 growth in scale and ovules, now become seeds. 



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