Mitosis in Pellia 



In 1901 Davis (7) made a detailed study of mitosis in various phases of the life- 

 history of Pellia. Centrospheres were found during the early divisions in the ger- 

 minating spore, but could not be identified in the sporophyte or in later stages of the 

 development of the gametophyte. 



At this time it hardly seems desirable to make a more extended r6sum6 of the 

 literature, since it is still too incomplete and indefinite to warrant generalizations. In 

 presenting our own results, we shall occasionally refer to the preceding papers and also 

 to papers dealing with mitosis in other groups. 



MATERIAL AND METHODS 



Most of the material for this work was collected near Bonn in Melbthal and in 

 the Siebengebirge. Early in October the spore mother-cells of Pellia are already 

 quite deeply lobed, and occasionally a sporogonium is found in which the spores are 

 already formed. By the middle of November nearly all of the spore mother-cells have 

 divided and many of the spores have germinated. The winter of 1901-2, in the Rhine 

 Province, was a very mild one, and germination proceeded with only occasional inter- 

 ruption throughout the entire season. Material brought into the laboratory at any 

 time after the middle of November developed much more rapidly than in the open, and 

 would shed the spores within a week or ten days. 



Before placing the material in the fixing agents, the calyptra was dissected away 

 and about one-third of the sporogonium cut off with a razor, thus freely exposing the 

 spores. In a few cases the mass of spores, held together only by the elaters, was 

 removed from the sporogonium, but while not nearly so many spores were lost as might 

 be anticipated, this tedious method was found to be unnecessary, since the other pro- 

 cess readily yielded smooth sections as thin as 2 /a or 3 /*. 



Several fixing agents were used, but only two gave thoroughly satisfactory results. 

 These were chromo-acetic acid (0.8g. chromic acid, O.Sc.c. glacial acetic acid, lOOc.c, 

 water) and a modification of Flemming's solution (0.5g. chromic acid, 0.5g. glacial 

 acetic acid, 1 per cent, osmic acid lOc.c, water 100 c.c). While achromatic structures 

 stain more readily after solutions containing some osmic acid, equally good prepara- 

 tions were often obtained from material fixed in the former solution. 



Most of the sections were cut at 2fi or Sfi, but sections 5/*, and even 10 fi or 15/a, 

 in thickness were used in determining the number of asters and in counting chromo- 

 somes. 



Haidenhain's iron alum hsematoxylin, with or without a slight tinge of erythrosin, 

 Congo red, or orange G, gave fairly satisfactory preparations, but gentian violet proved 

 to be so much superior in differentiating kinoplasmic structures that safranin and gen- 

 tian violet, sometimes with the addition of orange G, were used in most of the work. 

 Sections were stained, usually over night, in safranin (Ig. safranin in 100 c.c. of 50 per 

 cent, alcohol), then washed in 50 per cent, alcohol until all red color was removed 

 from the achromatic structures, and then stained for one or two hours in gentian violet 



330 



