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SEXUAL REPRODUCTION IN THE RUSTS. 
A. H. CHRISTMAN. 
(WITH PLATE VII1) 
THE nature of the aecidium has remained one of the most vexed 
questions in mycology. BLACKMAN’s' recent discovery goes far 
toward clearing up the most important points and my own results, 
described below, confirm his general conclusions, though showing a 
widely different method of conjugation. The literature relating to 
sexuality and the general cell processes in the rusts has been so thor- 
oughly and justly reviewed and critically estimated by BLACKMAN 
that I need hardly devote further space to it here. 
My studies on the winter conditions of the rusts and the nature 
of the aecidium led me to the preparation of material for cytological 
study, and in the spring of 1904 Professor J. C. ARTHUR proposed 
to Professor HARPER to furnish material from his cultures for cyto- 
logieal investigation. This material was turned over to me. It 
consisted of a quantity of carefully identified aecidia of several rusts, 
and since our knowledge of the method of origin of the binucleated 
condition found in the aecidiospores was at that time entirely lacking 
as to the details of the behavior of both cells and nuclei, my study 
was directed largely toward that point. 
It was soon found that aecidia of the caeoma type, with unlimited 
Stowth, were by far the most favorable material. This type of 
development apparently admits of less crowding of the hyphae, and 
as a result the cells and their relations can be made out more easily. 
Two forms were further found especially favorable because of the 
large size of their cells and nuclei. These were Caeoma nitens S. 
Stowing on Rubus cult., and Phragmidium speciosum Fr. on Rosa 
humilis, 
The best fixation was secured by the use of Flemming’s fixing solu- 
tions; both the strong and weak were very satisfactory. Fixing 
Solutions were sent to Professor ARTHUR and the specimens were 
I 
BLackman, V. H., On the fertilization, alternation of generations, and general 
Cytology of the Uredineae. Annals of Botany 18:323-373- pls. 21-24. 1904. 
“ 1995] 267 
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