452 The Botanical Gazette. [December, 
the presence of the favorable element sulphur, not present in 
potassium cyanide. Again, while bi-chromate of potassium 
is extremely injurious, chrome alum is rather favorable, which 
may be explained by the fact of there being such a small pro- 
portion of chromium in the latter compound, compared with 
its amount in the former. The effect of the element nitrogen 
is hardly determined by these experiments, but the majority 
of the facts seem to point to its being injurious, since its pres- 
ence in alkaloids makes the only difference, as far as mere 
composition is concerned, between these compounds, which 
are injurious, and the carbohydrates which are favorable; and 
since it is the greater constituent, by weight, in the unfavor- 
able radical, cyanogen. The correctness of this idea would 
tend to overthrow the opinion, often expressed, that an exX- 
cess of nitrogenous compounds in soils is favorable to the 
growth of rust. Another conclusion to be derived from the 
results of these experiments, is (4) that potassium sulphide 
be entirely useless for the prevention of rusts, since the 
spores grow readily in solutions of these compounds, even 
with the latter in a solution of 1:100. 
r. E. Wiithrich,* the only one, as faras I know, who has 
experimented in this same line, has had results very similar 
to my own, in so far as he has reported them. In his expefl- 
ments with uredospores of Puccinia gramints Pers., germin 
ation took place in a solution of potassium nitrate of fifty pet 
cent. strength. I did not use this salt at all, but it will be 
noted that it contains the favorable element, potassium, that 
I have already mentioned. On the other hand, he has oe 
reported the employment of potassium bi-chromate, one | 
salts having the most injurious effect upon germination 1) my 
own experiments. But where we have used the same com- 
pounds, the results have been practically the same. 
2. Witality and vigor of the summer spore-forms. 
Uredospores and zcidiospores have much greater pows 
of endurance than have usually been ascribed to them. re 
rich, in his article above cited, makes the following stateme #3 
with respect to the resistance of uredospores of Puccinta gf 
; . jgkeit 
“Ueber die Einwirkung von Metallsalzen und Sauren auf die Keimfahigke! 
der Sporen einiger der verbreitesten parasitischen Pilze unserer Kulturp’ 
Zeits. f. Pflanzenkrankheiten 1 (1892). 84-86. 
