Using the Microscope 



283 



a pollen grain put the preparation on the stage, using the same 

 objective and ocular micrometer, and note how many spaces a pollen 

 grain covers. If the pollen grain covers five spaces, its diameter is 

 five times 15 . 3 ju, or 76 . 5 /j.. In the same way, the value of a space 

 in the ocular when used with the other objectives should be de- 

 termined. The values for three or four objectives may be written 

 upon an ordinary slide label and pasted upon the base of the micro- 

 scope for convenient reference. 



*& U - 



be, 4ila^ I a . 



'ffi lew &t HO <GHC( miviJrr ^ SO 



(Be. 

 x52ff 



FIG. 104. Scale card for practical use. The figure is considerably smaller than the 

 card from which it was made. 



This method is the best one for measuring spores and for most 

 measurements in taxonomy. 



Measuring by Means of Camera Lucida Sketches.- -This 

 method is of great importance in research work, because vari- 

 ous details can be measured with far greater rapidity than 

 by the other method. Upon a piece of cardboard, about as 

 thick as a postal card, draw a series of scales like those shown in 

 Fig. 104. 



Make a scale for each objective. It is not necessary to make 

 scales for all the oculars, but only for the one in most constant use. 



