PREPARATION OF SPECIMENS OF OPUNTIA. 283 



thick. Outer sections can then easily be pressed down on the 

 edges and the soft rind cut out with a knife, leaving little but 

 the dished epidermis, which when flattened out shows much of 

 the tubercular and areolar arrangement. The sections from the 

 center show the relation of the pulp and rind rather imperfectly, 

 it is true, but still they give characters of value. 



Tracings of the fruit should always be made when they are 

 put in press. The fruit is cut through the middle lengthwise. 

 It has been my plan to lay this cut surface on the page of my 

 note book and trace its outine with a pencil and then, with the 

 specimen before me, draw in a line representing the outer margin 

 of the seedy pulp. Often a section is cut out of the center in- 

 stead of simply taking half of the fruit for the tracing. The 

 pencil point can then be punched through the edge of the pulp 

 at three or four points so as to guide one in outlining the pulpy 

 center. This tracing, easily made, shows graphically and ac- 

 curately the outline of the fruit, the shape of the apex, the relative 

 thickness of the rind and the exact color, which is transferred to 

 the paper as the tracing is made. With a little additional care 

 the stain on the sheet can often be made to show the relative 

 density of color of rind and pulp, all of which are of taxonomic 

 importance. 



All of this relates to specimens intended for the herbarium 

 sheet. Of course, fruits can be preserved for a time and most 

 species indefinitely in fluid, but the colored parts lose all of their 

 color, the liquid must be changed occasionally, and it is a constant 

 source of annoyance and inconvenience. 



A large part of the old survey material consists of joints dried 

 in the open air without pressure. This is a very slow process, 

 and while satisfactory so far as showing the spine arrangement 

 is concerned, the specimens must be kept in boxes, flowers must 

 be separated from their joints in the herbarium, and the color is 

 scarcely so well preserved as in pressed specimens. 



Of course, the more field notes one can take the better. When- 

 ever time permits, it is my practise to write quite as full a de- 

 scription as the condition of the plants will warrant. These 

 notes are always much more satisfactory than any drawn from 



