Thallophyta and Bryophyta 151 



the purchaser. Such materials will yield excellent preparations by the 

 methods recommended in Chap. 10. 



Few of the algae are microtomed for making slides. Some selected 

 items that are customarily microtomed are discussed briefly. 



CHARA AND NITELLA 



The growing points of CJiara and the sex organs of mature plants 

 must be sectioned to show cellular organization and nuclear structures. 

 Kill in medium I chrome-acetic or Craf II. These fluids contain 

 enough acid to remove much of the troublesome incrustation. The 

 condition of the material after 1 week in the fluid can be easily 

 ascertained by examining a whole mount. If abundant material is 

 available, several variations of these formulas should be tried, and 

 the batch having the best fixation used for embedding. Older oogonia 

 and zygotes are not readily penetrated by the above fluids; FAA 

 should be used. 



These plants become very brittle in xylene, but they section satis- 

 factorily after the butyl alcohol process. Examine small samples dur- 

 ing the process, thereby saving further work if a batch has undergone 

 plasmolysis. Infiltration should be gradual, with the time interval in 

 the oven reduced to 2 days or less. The staining of different batches 

 is highly variable. Try iron hematoxylin and safranin-fast green. 



Fucus and similar bulky forms are usually sectioned to show game- 

 tanaia. Kill in medium II or strong chrome-acetic made up with sea 

 water. Dissect out some of the gametangia to ascertain which fluid 

 preserves them best at the given stage. Process in TBA or dioxan. 

 Sections are difficult to affix to the slide. It may be necessary to use 

 an alcoholic bulk stain with some batches. Brilliant staining of imma- 

 ture sperms in the antheridia of Fucus has been obtained with iron 

 hematoxylin; sharp staining of nuclei during cleavage in the oogon- 

 ium is very difficult. 



The more massive Rhodophyceae that cannot be satisfactorily 

 made into whole mounts may be sectioned by the method given for 

 Funis. Since the great majority of readers do not have access to fresh 

 plants, the purchase of carefully preserved material from reliable col- 

 lectors is recommended. 



Fungi 



The processing of fungi involves many problems that are com- 

 mon to other categories of previously described subject matter. For 

 example, in processing a fungus parasitic on a leaf, the tissues of the 



