102 METHODS IN PLANT HISTOLOGY 



the material, in the center of the slide, taking care not to put on so 

 much that there will be a confusing tangle. Use scissors constantly so 

 as not to injure filaments by trying to tease them out. Put on a round 

 cover. There should he just enough glycerin to come to the edge of the 

 cover-glass, but not any more, for it is impossible to seal a mount if 

 glycerin has oozed out beyond the cover. 



The mount should now be sealed. Canada balsam, various asphalts, 

 cements, fiat varnish, gold size, and other things have been used. 

 Canada balsam is always at hand and seems to be as good as any. 

 Preparations which had been sealed with gold size more than fifty 

 years before have been exhibited in perfect condition, but they must 

 have been hidden away in some museum, for a glycerin mount would 

 never survive fifty years of laboratory use. The gold size, as painters 



L 



Fig. 19. — Slide, natural size, showing size and form of ring 



use it, is likely to be too thin for sealing mounts. Put some of it in a 

 1-ounce bottle with a wide neck and leave the cork out until the gold 

 size thickens a little. Should it become too thick, thin it with turpen- 

 tine. 



Nothing but practice will enable one to spin a good ring, but a good 

 camel's-hair brush, a good turntable, and a balsam neither too thick 

 nor too thin will facilitate matters. Gently touch the cover and slide 

 at three or four points with the tip of the brush, so that a very small 

 drop of balsam will bind the cover to the slide. In half an hour the tiny 

 drops of balsam will have hardened sufficiently for the next step, the 

 spinning of the ring. Clip the slide to the turntable so that the cover 

 glass is perfectly concentric with the rings, give the turntable a gentle 

 spin, and with the brush touch the shde as far out from the cover as 

 you wish the ring to extend, then gradually approach the cover. Dip 

 the brush in the balsam again, and gradually extend the ring until it 

 is about iV 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 Hkely to be broken, and thick rings are in the way if 

 the preparation is to be examined with high powers. A medium ring is 



