FUNGI 



267 



black-rust stages. When found, it may be so abundant that most of 

 the leaves of the barberry are spotted with the cluster cups. It is a 

 curious fact that wheat and oats may be quite free from the red and 

 black rust in localities where the aecium stage is very abundant, and 

 that the rust stages may be most destructive where there are no bar- 

 berry bushes. But not all rusts of wheat and oats are Puccmia grami- 

 nis, and other rusts have other hosts than the barberry for the aeci- 

 um stage. However, Puccinia graminis is so prevalent and destructive 

 that there is some excuse for the campaign for eradicating the common 



Fig. 71. — Puccinia oraminis: photomicrograph of aecium stage on barberry. Fixed in chromo- 

 acetic acid and stained in cyanin and erythrosin. Eastman Commercial Ortho film, Wratten E 

 filter (orange); arc light; Spencer 16-mm. objective, N.A. 0.25; Bausch and Lomb projection eye- 

 piece; exposure, j second. X-17. Negative by Dr. P. J. Sedgwick. 



barberry. No one doubts that the aecium on barberry is a stage in the 

 life-history of Puccinia graminis. 



The aecium on barberry cuts easily in paraffin (Fig. 71). Formalin 

 acetic alcohol (formalin 10 c.c; acetic acid, 5 c.c; 70 per cent alcohol, 

 85 c.c.) fixes well. If a chromic solution is used, cut a piece from each 

 side of the sorus, keeping about the middle third, since the fixing agent 

 does not penetrate well. Iron-alum haematoxylin is the best stain to 

 bring out the binucleate condition in the aeciospores. 



If the aecium stage is not easily available, there are various aecia 

 which are just as good, or even better, for morphological study. The 

 aecia growing on Euphorbia maculata (spotted spurge) are abundant 

 and are very easy to fix and cut. The infected plants are also very 



