286 Trans. Acad. ScL of St. Louis. 



to finish the work since coming here. I am indebted also to 

 Dr. Trelease of St. Louis for material and the use of his 

 excellent library. 



Material and Methods. 



Fern prothallia may be found very abundantly in any green- 

 house where ferns are kept. Most of my material was col- 

 lected in the greenhouses of Lake Forest and belonged to the 

 genera Adiantum and Aspidium. Young ferns were grown 

 from part of the material collected and found to be species 

 belonging to these two genera. Since working in Missouri 

 State University I have twice succeeded in collecting material 

 in the field under natural conditions. In both cases the pro- 

 thallia grew at the mouth of caves and belonged to the species 

 Woodsia obtiisa. I have also obtained prothallia of the same 

 species from the Missouri Botanical Garden at St. Louis 

 through the kindness of Professor Trelease. I have kept such 

 material in the laboratory under a bell jar where fertilization 

 was accomplished and young ferns were rapidly developed. 



To get stages of fertilization in these forms I have found 

 that putting a considerable number of prothallia, removed from 

 the soil as carefully as possible without injury, into a watch- 

 glass and filling it half full of water, gives the best results. 

 They are left in water from an hour and a half to three hours. 

 The shorter time has given the more satisfactory results. The 

 longer times have given figures which seem to be question- 

 able. The archegonia seem to be overstimulated so that 

 cases apparently occur where they open before fully ready 

 for fertilization. Antheridia also seem to burst before the 

 spermatozoids are fully ripe, so that stages where either con- 

 dition occurs are at least questionable. Killing and fixing has 

 been best accomplished in Flemming's weaker chrom-osmiura- 

 acetic mixture allowed to act for thirty to forty-eight hours. 

 The material was then dehydrated and imbedded in paraffin. 

 Shrinkages sometimes occurred, but my figures show that in 

 my best preparations they were extremely slight and in 

 many cases not to be detected at all. The sections 

 were cut five microns in thickness and stained with the 

 Flemming triple-stain safranin, gentian violet, and orange 



