28 



HOW TO PHOTOGRAPH 



leaves are immersed in the fluid, it is best 

 to wash them in clean water with a soft 

 brush, since all leaves are more or less cov- 

 ered with fine dust, which will sink into 

 their substance if not removed when they 

 are fresh. When they are quite clean, 

 they may either be put in the bleaching 

 liquid at once, or put between clean blot- 

 ting paper to dry. Dried leaves, as a rule, 

 bleach more rapidly than green ones. 



When a leaf happens to be more deeply 

 colored than usual, it is a good plan to im- 

 merse it in alcohol until most of the color 

 has been removed. This much facilitates 

 the bleaching process. The time which tis- 

 sues require to be soaked varies considera- 

 bly. Some becomes translucent in a few 

 hours, while others take many days ; others 

 will show green patches which obstinately 

 refuse to be bleached. In this case, remove 

 the leaf, wash ii well, and place it in alco- 

 hol for some hours. In this way all the 

 chlorophyl will be dissolved out, when the 

 soda solution will complete the processes. 

 Care must be taken not to put too many 

 leaves at a time into one vessel ; three or 

 four is the average number. 



When properly translucent, the leaves or 

 tissues must be removed from the soda so- 

 lution, and washed in distilled water, chang- 

 ing the water every few hours. If the tis- 

 sues do not contain Raphides, the addition 

 of a little hydrochloric or nitric acid to the 

 second or third washing will increase their 

 transparency. Sulphuric acid must not 

 be used, or crystals of sulphate of lime, 

 which is only slightly soluble in water and 

 acids, may be formed in the tissues, and 

 cannot be removed. 



About twenty-four hours is necessary to 

 properly wash the leaves ; less time is not 

 sufficient, and a longer immersion tends to 

 disintegrate delicate tissues. The washing 

 completed, they should be placed in alco- 

 hol, in which they must remain for some 

 hours, and afterwards be transferred to tur- 

 pentine until required for mounting. 



The above bleaching process must be ap- 

 plied to sections of wood which are too 

 strongly colored for photography. It is 

 hardly necessary to observe that all sections 



which are to be photographed should be of 

 extreme thinness. Many which answer very 

 well for examination under the microscope 

 are far too thick for the photo- microgra- 

 pher. Light-colored sections, such as those 

 of white pine, require merely saturation with 

 benzole before mounting in the balsam solu- 

 tion. A section of deal, to show the char- 

 acteristic "discs," should be mounted dry. 



Spiral vessels, scalariform tissue, etc., 

 will require but little treatment ; the former, 

 after drying and washing in alcohol and 

 benzole, may at once be set up in balsam. 



Cuticles may be prepared in the same 

 way. In the case of very transparent tis- 

 sues, staining will be of great use. Jud- 

 son's dyes answer very well for this pur- 

 pose, but all blue stains should be avoided 

 in objects intended for photo-micrography. 



Plant-crystals, or raphides, moy be pre- 

 pared either in situ, or separately. When 

 mounted in situ, bleaching with alcohol is 

 alone admissible. Raphides may be ob- 

 tained from most plants by laying a leaf or 

 stem on a slide, with the cut end about the 

 middle ; a gentle rolling pressure with a 

 pencil will squeeze thejuice and raphides out 

 on the glass. Wash with alcohol, pour 

 over a little turpentine, and mount in the 

 usual way. 



The following furnish good examples of 

 raphides : duck weed, the onion, the wil- 

 low-herb, the galium or goose-grass. The 

 large prismatic crystals of the onion or 

 garlic i)olari?,e splendidly, and show better 

 in a photograph when polarized light is 

 used. In fact, many objects that are far 

 too transparent to make good photographs 

 can be easily managed by putting on the 

 polariscope. When this is of no use, a 

 piece of fine ground glass, or oiled paper, 

 immediately below the slide will be of great 

 service in softening the light. This will 

 prolong the exposure, but give results that 

 could not otherwise be attained. 



For instruction as to staining vegetable 

 tissues, the student is referred to a very 

 valuable and practical paper by Dr. George 

 D. Beatty, which appeared in Science Gos- 

 sip for May, 1876 ; also to Practical Mi- 

 croscopy, Chapter 12. 



