39S BOTANICAL GAZETTE [may 



of paraffin, corked, and set aside and not disturbed until the satura- 

 tion point is reached. The container is next placed on the oven 

 until the new saturation point is reached, next in the oven, and 

 imbedding is proceeded with in the usual manner. Even here, when 

 dealing with delicate plants, the xylol-parafhn is poured off only 

 to the wire gauze and the container again filled with blocks of 

 paraffin. 



By this method paraffin is slowly dissolved, and as it descends is 

 slowly and uniformly diffused through the xylol, thus preventing, 

 in a large measure, damage to the object by rapid changes in density. 

 It takes longer to reach the saturation point than when solid par- 

 affin is permitted to fall to the bottom of the container, but little 

 plasmolysis results. 



Using delicate liverworts for test objects it was found that no 

 deformation of tissue took place, except that which can be accounted 

 for by the excessively large coefficient of expansion (0.00027854) of 

 paraffin. The deformation caused by paraffin in an artificial cell 

 was found to be exactly the same as is always present in plant cells 

 when the paraffin is quickly cooled. 



Many workers use a very close series of alcohols in dehydrating 

 and a similarly close series in replacing alcohol with the paraffin 

 solvent, and then undo all their careful work by indiscriminately 

 adding paraffin to the solvent. 



A method of fixing paraffin ribbons to the side with certainty 



Albumen fixative, which is almost universally used to fasten 

 paraffin ribbons to the slide, has many excellences and a few disad- 

 vantages. Among the latter is the property of coagulating when 

 subjected to moderate heat, and in consequence losing its adhesive 

 quality. Because of this it is sometimes impossible to use sufficient 

 heat to straighten refractory or much wrinkled ribbons, especially 

 if paraffin melting at 58-60 is used. Again, it is almost impossible 

 to fix sections of certain refractory plants to the slide, even if the 

 ribbons are first straightened by floating on warm water and then 

 transferred to an albumen coated slide and allowed to dry without 

 heating. This is particularly true of sections of antheridial and 

 archegonial heads of some mosses and of the strobili of Selaginella. 



