1894 THE 3IICR0SC0PE. V 



The majority of foliage leaves can be used, if it is de- 

 sired to secure exact reproductions of their patterns of 

 venation. Of many orders, such as Rosaceae, Legumin- 

 0S8B and. Grramine^T, most of the leaves have veins suffi- 

 ciently translucent to admit of their being used as neg- 

 atives, without any preliminary preparation — even pre- 

 vious pressing and drying not being necessary. 



But in case of many leaves of the orders Compositsp^ 

 Ericaceae, Umbellifer??, etc., they must be subjected to a 

 process of bleaching in alcohol, followed by immersion 

 in hot potassic hydrate ; this is to be followed by thor- 

 ough washing in pure and finally acidulated water, and 

 pressing the leaves till dry between sheets of bibulous 

 paper. Such prepared leaves will give pictures in which 

 the veins and veinlets are dark and the remainder of the 

 leaf light colored, just the reverse of the photographs 

 obtained by using the fresh or dried leaves without fur- 

 ther preparation. In either case the venation — even in 

 minutiae — will be well shown. 



Sometimes young leaves, in other cases fully matured 

 leaves, give the best results. Leaves from the herba- 

 rium can be used at will. If the veins or petiole are 

 very much thicker than the remainder of the leaf, they 

 can be shaved down. Other specimens may, in some 

 cases, need trimming. 



It is necessary that the object to be photographed be 

 brought into very close contact with the sensitized paper, 

 for, otherwise, all parts of the print will not be perfectly 

 distinct. For this reason, the under side of the leaf — 

 where, as a rule, the veins are more prominent — should 

 be placed next to the clear glass in the printing frame, 

 and the upper surface next to the sensitized paper. A 

 layer of cotton or soft blotting paper can be placed over 

 the back of the sensitized paper, which will insure closer 

 contact with all parts of an object that may be some- 

 what uneven. 



