NOTES AND ABSTRACTS* 
209 
the organism is seen to increase. In soil under orchard conditions the organism 
disappears even more rapidly than in soil in boxes or culture tubes. Seeds 
planted in pots of soil naturally infected with the canker develop normally 
without any canker. This author holds that the organism may live on buried 
leaves or woody roots, and suggests these as possible sources of holding the 
canker organism alive over the winter. 
The author of the second paper agrees that the organism undergoes a rapid 
and continuous decline in numbers under normal soil conditions. The vanishing 
point is reached in about two weeks by the test methods employed. These included 
rendering soil alkaline with lime-water, or by lowering its temperature or 
sterilizing by steam. The addition of dilute sulphuric acid also causes the 
organism to disappear. 
In water the decline is more marked than in soil. Certain bacteria have a 
marked deleterious effect on P. citri in artificial culture media, both by in- 
hibiting growth and by killing it. The fungus apparently enters the seedlings 
by wounds only. — A. B, 
Citrus Canker (Pseudomonas citri). By Geo. L. Peltier (U.S.A. Jour. 
Agr. Res. xx. No. 6, Dec. 1920, pp. 447-506). — The susceptibility and resist- 
ance of a large number of Rutaceous plants to citrus canker are influenced by 
the following factors : the anatomical structure of plants, the reaction of the 
host plants to their environment, the influence of external conditions on the 
organism and its susceptibility to infection, and the influence of the host upon 
the virulency of the organism. The author finds that the temperature relations 
of Pseudomonas Citri Hasse in culture is similar to those of the Pseudomonas 
group of bacteria. The minimum temperature for growth in culture is about 
5 0 C, the optimum between 20 0 and 30 0 , the maximum about 35 0 for 24 hours, 
and a thermal death-point between 49 0 and 52 °. Humidity is closely associated 
with temperature and has marked effect upon the viability of the organism. At 
low temperatures, humidity has little or no influence, while at high temperatures 
and high humidity it is the limiting factor. 
The Citrus plants used vary markedly in their reaction to temperature and 
humidity, the optimum being between 20 0 and 30 0 C. Three conditions necessary 
for infection : free moisture on the plant, suitable temperature, and an actively 
growing plant. The conditions for rapid plant growth are also the same for rapid 
development of the disease. When the host plant becomes dormant the organism 
becomes inactive and quiescent. 
A short bibliography is given. — A . B. 
Citrus Scab Fungus. By H. S. Fawcett (U.S.A. Jour. Agr. Res. xxi. 
No. 4, May 1921, pp. 243-252). — The author shows by his experiments that 
the conditions necessary for scab infection by Cladosporium citri on Citrus auran- 
tium are (1) Viable spores of the fungus, (2) young citrus leaves of a susceptible 
species, (3) moisture, (4) temperatures between i6°C. and 23 0 C. — A. B. 
Citrus Trees, Collar Rot. By C. O. Hamblin (Agr. Gaz. N.S.W. xxxi. 
pp. 439-441 ; 6 figs.). — Collar rot in citrus trees is due to a fungus (Fusarium 
limonis) which causes gumming of the tree near the ground. The remedy 
consists in laying bare the base of the tree and applying to the wounds a paste 
composed of copper sulphate, i|lb., quicklime, 4 lb., and 1^ gallon of water. 
' S. E. W. 
Citrus Trees, Spraying for the Control of Insects and Mites attacking in 
Florida. By W. W. Yothus (U.S.A. Dep. Agr., Farmers' Bull. 933, March 1918 ; 
24 figs.) — -This bulletin gives information regarding the best equipment for 
Florida conditions, and directions for preparing effective home-made insecticides. 
There is also a spraying schedule that has proved satisfactory after several 
years of practical experience. — V. G. J. 
Codling Moth, A Quandary and a Query. By G. W. Herrick (Journ. Econ. 
Entom. vol. xiv. pp. 1 56-160 ; April 1921). — It is well known that a large number 
of codling moth larvae enter the young fruits through the side, in addition 
to those which enter by the calyx. The percentage entering by the side is 
sometimes as high as 66-96 per cent, of the infestation, but appears to vary 
with different varieties of apple, and the degree and earliness of closing of the 
calyx incident on the season and the variety concerned. It is emphasized 
that, in consequence, a second or even third spraying with arsenate of lead may 
be a profitable measure. Another control recommended is the removal of 
fruits entered by the side at the time of thinning. Such apples may be detected 
by a small quantity of frass extruded by the larva. — G. W. G. 
Copper-Spray Coatings, The Field Testing of. By J. R. Winston and H. R. 
Fulton (U.S.A. Dep. Agr., Bull. 785, March 1919 ; 4 figs.).— This field method 
