139 



^POLLEN GRAINS 



OBJECT-HOLDER 



Fig. 258. Plastic unit with ready-made pyramid. (N.B. The pyramid is 

 enlarged about 10 times, the rest of the figure about 3 times.) 



is low, the dimensions of the pyramid, with a view to increasing the 

 number of pollen grains to be sectioned, must be larger). The total height 

 of the pyramid should not exceed half a millimetre if sections of a thickness 

 of about 0.25-0.50 // are to be made). These recommendations have been 

 followed when working with the modified Spencer microtome model 821 

 and are not always valid for ultra-thin sectioning. 



The best results are obtained by working with samples rich in pollen 

 grains and absolutely clean. Organic debris renders cutting more difficult, 

 shreds the sectioned pollen fragments, or covers them, and decreases the 

 value of the sections on the whole. Inorganic material (e.g. silicon or other 

 mineral particles) will damage the microtome knife. 



Fig. 260 illustrates the order, directions etc., to be followed when mould- 

 ing the pyramid, but it goes without saying that there can be many modi- 



PLASTIC 



SECTIONED POLLEN 



Fig. 259. Section from the basal part of the pyramid, x 100. 



10-565617 G. Erdlman 



