Freehand Sections 91 



alcohol 1 minute, absolute alcohol 2 to 5 minutes, clear in clove oil or 

 xylol, and mount in balsam. It is a good plan to put at least three 

 peristomes on a slide, one with the outside up, one with the inside up, 

 and another dissected to show details of the teeth. 



Fairly good unstained mounts of the archegonia and antheridia 

 of small mosses can be obtained by following the directions for 

 mounting the sori of ferns. 



Beautiful and instructive mounts of the more delicate foliose 

 Jungermanniaceae can be made by staining lightly in Delafield's 

 haematoxylin whole plants, or pieces as long as can be covered con- 

 veniently. The method is that just given for fern prothallia. The 

 mount should show both dorsal and ventral views. 



The Epidermis shows its best surface views without sectioning. 

 Select some form with large stomata, like Lilium or Tulipa, strip 

 pieces of epidermis from both sides of the leaf, and place them imme- 

 diately in absolute alcohol for 1 or 2 minutes. Stain in Delafield's 

 haematoxylin; after this stain is satisfactory and all acid has been 

 washed out, stain for 1 or 2 minutes in aqueous eosin, erythrosin, or 

 acid fuchsin; place directly into 95 per cent alcohol for a few seconds 

 (merely to save the absolute alcohol), then into absolute alcohol for 

 about 30 seconds, and then into clove oil. Mount in balsam. The 

 epidermis is likely to curl and, unfortunately, patience seems to be 

 the only remedy. In mounting, be careful to get pieces from both 

 sides of the leaf, and be sure that the pieces are outside up. The 

 inside of the epidermis is usually more or less rough, on account of 

 the mesophyll torn off with it. Sedum purpurascens will show 7 vari- 

 ous stages in the development of stomata, even in epidermis stripped 

 from mature leaves. 



Other Objects.- -The cases just given will suggest other objects 

 which might be mounted by this method. In Part II of this book 

 this method is frequently recommended for mounting certain struc- 

 tures. Aside from the tediousness of the method, the principal 

 objection to it is the danger from plasmolysis. 



Nearly all objects which used to be mounted in balsam without 

 sectioning are now handled more successfully by the Venetian tur- 

 pentine method. Consequently, the method just described stands 

 just where it was ten years ago. 



