l86 CALIFORNIA ACADEMY OF SCIENCES. 



as the whole sorus could be handled, and imbedded, and 

 sections made, which would, of course, have been out 

 of the question were the microspores allowed to become 

 entirely separate. Gradually, however, the walls of the 

 indusium soften and most of the spores are forced out 

 into the water by the swelling of the mucilaginous matter 

 that surrounds them. 



The structure of the fruit and the development of the 

 sporangia and spores have been exhaustively studied by 

 Russow,* and it is only necessary to state here that up to 

 a late stage of development, the sporangia and spores 

 develop alike in the two sorts of sporangia, but that later 

 in the macrosporangium one of the young spores finally 

 grows at the expense of the others, which are gradually 

 absorbed b}^ it in its growth, and finally fills the whole 

 sporangium. In the microsporangium, all of the original 

 sixty-four spores come to maturity. 



In studying the spores they were first treated for about 

 two hours with a i per cent, aqueous solution of chromic 

 acid, and after repeatedly washing in distilled water to 

 remove as much of the acid as possible, were gradually 

 brought into 95 per cent, alcohol where they were allowed 

 to remain until wanted. By this means the acid was com- 

 pletely removed, and they stained readily with cochineal 

 or carmine solution, which will not act satisfactorily if 

 an}^ acid is left in the specimens. After staining with 

 alum-cochineal, the specimens were dehydrated, imbedded 

 in paraffine, and cut with a Minot microtome. Before 

 finally mounting, they were further stained on the slide 

 with Bismarck brown (in 70 per cent, alcohol) and mounted 

 in Canada balsam. Specimens thus treated show very 

 beautifully all the details of cell-division, and enabled me 



"Russow. Histologic und Entwickelungsgeschichte der Sporenfrucht von 

 Marsilia. Dorpat, 1871. 



