94 Methods in Plant Histology 



too thick nor too thin will facilitate matters. Give the turntable a 

 spin, and with the brush touch first the slide about as far out from the 

 cover as you wish the ring to extend, then gradually approach the 

 cover. Dip the brush in the gold size again, and gradually extend 

 the ring until it is about one-sixteenth of an inch wide on the cover. 

 The touch must be extremely gentle or the cover will be moved. Do 

 not try to put on a thick ring the first time, but let a thin ring harden 

 for an hour (months would do no damage), and then a thicker ring can 

 be added without any danger. Thin rings are too likely to be broken, 



FIG. 18. Slide, natural size, showing size and form of the ring. 



and thick rings are in the way if the preparation is to be examined 

 with high powers. A medium ring is best, and it should consist 

 of two coats, for a crack would seldom appear at the same place 

 in both coats. A good shape and thickness for a ring are shown 

 in Fig. 18. 



The following is a summary of the foregoing processes: 



1. Fix in chromo-acetic acid, 24 to 48 hours. 



2. Wash in water, 24 hours. 



3. Iron solution, 2 hours. 



4. Wash in water, 20 minutes. 



5. ^ per cent haematoxylin, 3 to 24 hours. 



6. Wash in water, 20 minutes. 



7. Iron solution until stain is right. 



8. Wash in water, 1 to 4 hours. 



9. 10 per cent glycerin. 

 10. Mount and seal. 



If the material has been fixed in formalin, it should be washed in 

 water for 5 to 10 minutes before staining. Material preserved in 70 

 per cent alcohol should be placed successively in 50 per cent, 35 per 

 cent, 15 per cent alcohol, and then in water, allowing each to act 

 for 15 to 30 minutes before being placed in the stain. 



Mayer's haem-alum is also a good stain for filamentous algae 

 and fungi which are to be mounted in glycerin. The process, after 

 fixing and washing in water, is as follows: 



