54 THE ELEMENTS OF VEGETABLE HISTOLOGY 



patience and an aptitude which can only be acquired 

 by practice. While natural talent for drawing is an 

 advantage, it is not absolutely essential, and those 

 not so talented will often produce more exact sketches. 

 In sketching both eyes must be kept open and one 

 eye should be at the microscope while the other is 

 focused on the paper. Various parts of the specimen 

 should be examined and only the clearest objects 

 should be selected for drawing. One seldom finds satis- 

 factory fragments of different tissues in a single field, 

 and it is therefore necessary to explore a number of fields, 

 selecting suitable materials from each and combining 

 all in one drawing. Having decided upon the part 

 of the specimen to be drawn, one should roughly 

 plan it out on paper so that all parts of the object 

 will be in proper relation both as regards size and 

 position. The outlines should then be sketched in 

 and finally light shading may be employed to indi- 

 cate contrasts in depth of color. Particular attention 

 is directed to the following points: 



1. Each cell is entirely surrounded by a cell wall, and this is 



unbroken unless the specimen has been injured in prepara- 

 tion. In representing cell walls the lines should be 

 continuous and should be brought back to the starting 

 point. 



2. A cell wall has a certain thickness and this must be repre- 



sented by surrounding the cell with a double line or a 

 single line of substantial width. 



3. Cells rarely appear as exact geometrical forms (circles, squares, 



oblongs, etc.) although they may closely approach these. 

 There are slight but distinct differences between cells, 

 even though they are adjacent. In a drawing, each 

 cell should be fitted to the others in the tissue and the 

 slight differences in shape and size should not be over- 

 looked. 



