126 METHODS IN PLANT HISTOLOGY 



White of egg (active principle) 50 c.c. 



Glycerin (to keep it from drying up) 50 c.c. 



Salicylate of soda (antiseptic, to keep out bacteria, 

 etc.) 1 g. 



Shake well and filter through cheesecloth. It will keep from 2 to 6 

 months, but, to say the least, it is never better than when first made up. 



Put a small drop of fixative on the slide, smear it evenly over the 

 surface, and then wipe it off with a clean finger until only a scarcely 

 perceptible film remains ; then add several drops of distilled water and 

 float the sections or ribbons on the water. Warm gently until the par- 

 affin becomes smooth and free from wrinkles. Wrinkled or curved 

 ribbons may be straightened by touching with a needle at each end 

 and pulling gently, just as the ribbon begins to smooth out in the 

 warming. 



When the water is warmed, the ribbon almost always stretches. 

 Theoretically, it should not stretch at all, if the cutting has been per- 

 fect. If a ribbon cut at 10 /x does not lengthen more than 10 per cent, 

 the cutting is fairly good; if it lengthens 20 per cent, cut thicker sec- 

 tions or lower the temperature, using ice if necessary. If a 5/x ribbon 

 does not lengthen more than 10 per cent, the cutting may be regarded 

 as good; at 1 ^ or 0.5 /x, if it does not lengthen more than 20 per cent, 

 the cutting has been good. Be very careful not to melt the paraffin, be- 

 cause the albumen coagulates with less heat than is required to melt 

 the paraffin. Consequently, there would be nothing to fix the ribbon 

 to the slide. 



After the sections become smooth, remove as much of the water as 

 possible. This precaution is usually neglected. Drain off what you can. 

 Then, by touching filter paper to the edge of the sections, get rid of 

 some more water. As the water is removed by the filter paper, the 

 edge of the ribbon comes first into contact with the slide and thus 

 seals in some water. Touch the edge of the ribbon with a hot needle 

 and use the filter paper again. If care be taken at this point, there is no 

 danger later, even when using stains requiring 24 or even 48 hours in 

 liquids. This may seem slow and tedious, but when you compare a 

 slide of mitosis in root-tips, or the reduction divisions in pollen mother- 

 cells put up this way, with the usual hasty preparations, you will see a 

 difference. 



If you should heat the ribbon so hot as to melt it, some things can 

 be saved by cooling the ribbon and floating it off to another slide 



