90 Methods in Plant Histology 



wash in slightly acidulated water for a few seconds, and then wash 

 thoroughly in pure water. The prothallia must now be brought 

 through a graded series of alcohols, 15, 35, 50, 70, 85, 95, and 100 per 

 cent being sufficiently close to prevent plasmolysis. Then use 

 mixtures of alcohol and xylol, 3 parts absolute alcohol and 1 part 

 xylol, 2 parts alcohol and 2 parts xylol, 1 part alcohol and 3 parts 

 xylol, and then pure xylol. Then bring the sections into a mixture 

 of xylol and balsam, using at least 10 parts of xylol to 1 of balsam. If 

 left in a shell, without corking, the xylol will soon evaporate, so that 

 in a few days the prothallia may be mounted. Use the balsam in 

 which the material has been standing, because any other balsam may 

 have a different concentration. At every step in the process the 

 prothallia should be examined under a microscope, so that any 

 plasmolysis may be detected. If each succeeding step is tested with 

 a single prothallium, a general disaster may be avoided. If plas- 

 molysis takes place, weaken the reagent and try another prothallium. 

 When a safe strength is found, bring on the bulk of the material, and 

 use the same method with succeeding steps. The dangerous places 

 are likely to be the transfer from alcohol to xylol and the transfer 

 from xylol to balsam. The process is tedious, but the mounts are 

 very firm and durable. The Venetian turpentine method is less 

 tedious, and, in our opinion, gives just as good results. 



Sori of Ferns. Instructive mounts of sori or of individual 

 sporangia may be made without sectioning. It is better to choose 

 ferns with thin leaves, since leaves thicker than those of Asplenium 

 thelypteroides are likely to be unsatisfactory. If this fern is at hand, 

 cut off several of the small lobes which bear three to six pairs of sori. 

 Fix in chromo-acetic acid; wash in water; stain in Delafield's 

 haematoxylin, or omit staining altogether; pass through a series of 

 alcohols, allowing each grade to act for at least 10 minutes; clear in 

 clove oil, and mount in balsam. If the sori have begun to turn brown, 

 better views of the annulus will be obtained without staining. 



Mosses and Liverworts. Nearly all mounts are more successful 

 by other methods, for which the student should consult the chapters 

 on Bryophytes (chaps, xviii, xix). Excellent mounts of the peristome 

 of the moss can be made as follows: From fresh or preserved capsules 

 cut off the peristome just below the annulus. Treat with 95 per cent 



