374 



METHODS IN PLANT HISTOLOGY 



Measuring by means of camera lucida sketches. — This method is 

 of great importance in research work, because various 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 Figure 139. 



' . im 



^ 



lOVfJ 



20O/. 



h-t§ 



300h toof) I 



SOOtJ 



spencer /6mm. Oc./6 



Diamefer of field /joo/jjjmm. 



U 7L 3^0^ 9\)0u""^7- 



to 



Co 



fi 





I 5 



03 



Droiun at ki^el of fable ^^ c^^f 



§-.^^ 



.^ 





> 



I 



/Mirror bar af /OO 

 flirrorat^'' 







^ 



P>c;^^ 



09/ /y 



0//00 '^^(f ofuof)ij JGOued^ 



f 



h.-t' 



Ml A 



^nM'-^ 





Fig. 139. — Card scale for practical use 



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. It is 

 absolutely necessary to note the tube length, length of the bar of the 

 camera mirror and inclination of the camera mirror, and the level at 

 which the scale is made. A variation in any of these details will change 

 the scale. 



