142 BOTANICAL GAZETTE [FEBRUARY 
water. (4) Artificially prepared humus neither affected the N-fixation favorably, 
nor could the bacteria use it as a source of food. (5) The N-fixing power of 
supplies of Azotobacter derived from pure cultures and grown in identical con- 
ditions was extraordinarily different at optimal temperatures as well as at low 
and higher points. Some light may be cast on this by the following. 
In an elaborate examination of the behavior of Azotobacter'! THIELE believes 
that he has established incontestably that this organism is capable of accumulating 
N in the laboratory; but he is quite uncertain whether this power belongs specifi- 
cally to it, as for example alcohol production does to yeast. It is not impossible 
that N-starvation in the artificial culture or the stimulation by abundance of 
organic matter awakens an inherent capacity of Azotobacter to fix N, whic 
ordinarily slumbers. The growth of Azotobacter in artificial cultures is neither 
decisive nor typical. Its mode of action in the soil is still entirely unknown 
and is likely to remain so, in spite of theories, until there have been devised more 
exact methods of investigating the extremely minute variations of the N in soils. 
In view of all this uncertainty, Taree deprecates giving agriculturists any 
advice nae would lead them to attempt to sh ane Chili saltpeter by a bacterial 
*‘fertilize RK. B. 
Burbank’s work.—An interesting and illuminating account of the breeding 
experiments of LUTHER BurRBANK is contributed by DeVries to the Biolo- 
gisches Centralblatt.*? It is the first statement we have seen addressed to scientific 
men by a man competent to appreciate both the practical and scientific aspects 
of BuRBANk’s work.—C. R. B. 
Anti-enzyme.— With the aid of Berret, CzApeK" has now elaborated the 
results of ten years of research devoted to developing a chemical test for tropistic 
sensation. Until 1897, when the author published his initial paper of this inves- 
tigation, we had no way of knowing that an organ had perceived a stimulus unless . 
it manifested response in the form of a motor reaction. In fact it was assumed 
that perception had not occurred unless such a motor reaction followed. FITTING, 
in his work on tendrils, was able by indirect methods to show that an organ may 
perceive a stimulus and still be incapable of executing a motor reaction. In 
animal irritability it has long been believed that sensations involve alterations 
in the metabolism of the organ. To Czapex belongs the honor of a fruitful 
pioneer research. Root tips contain tyrosin, an unstable derivative of proteids, 
continually yielding oxidation derivatives. The most prominent of the latter is 
omogentisinic acid. This research has shown that this acid is present in unstim- 
1 THIELE, R., Die Verarbeitung des a sae glare Stickstoffs durch Mikro- 
organismen. Landw. Versuchs-Stat. 63:161—-2 1906. 
72 DE Vries, Huco, Die ae Luther Burbank’s. Biol. Centralb. 
ers ais 
3 CZAPEK, FRIEDRICH, unter Mitwirkung von RupoLtpH BERTEL, Oxydative 
ellvichtoncacs bei pflanzlichen Reizreaktionen. (Zwei Abhandlungen.) Jahrb. 
Wiss. Bot. 43:361-467. 1906. 
Siiigetin aimed me 
