(^\KNE — Broini Bot of Citru.^i. 
To ol)taiii couidia and oospoi'cs the best method adopted “was to 
on potato dextrose agar fairly large ])ieees of atfeeted leaf tissues. 
Pieces about 1 cm. srpiare have been used. Pruit tissues are less. 
eff(*ctive. From the edges of the ])lated i)ieces there is a strong 
growth of mycelium, while on the upper surface conidia are di*- 
veloped in great numbers. Within the tissues oos])ores are 
d(‘veloped in large uuml)ers shortly after the conidia aj)])ear. With 
sufficient care the growth is ])ractically ])ure. 
(’onidia may also be obtained by half submerging affected leaf^ 
twig or fruit fragments in water. Those develo])ed on the free 
surfaces are normal in sh.ape. An aquatic mycelium is (h'veloped u\ 
tii(‘ wat(‘r. This hears conidia ^vh^clL are ratluu* more liable to varv 
in sliaj)e, thougii not markedly so. 
Owing to lack ot ecpiipment it has not been ])ossibh“ to ast-er- 
taiii the limits and oi)tima of temperature and humidity for growth.. 
Jh)th fit'ld and laboratory evidence,, indicate a low temjH'rature o]di- 
mum and maximum. The (q)timum is ju-obably Itelow loo(’. and' 
th(‘ maximum below 2o° i\ Fresh occurrence.s in the field have- 
not be-.m noted later than October, or before iMav. even when Octo- 
ber has been exceptionally wet as in 102.‘>. or und(u- irrigation 
<-onditions. It should be noted that the mean maximum and mini- 
mum temperatures for Perth for the months in which the disease is 
evident are: — 
June .July Aug. 8e]ff. 
Max. 17.8° 17.00 (Vut. 
Min. 9.7° 8.7° 8.9° .10. 2o Cent. 
(Figures sti], plied by ( hnnmon wealth iUeteondogical Bureau.. 
Jhn-th). 
As tlu' mean foi' the affi'cti'd areas dui'ing these months i.> 
ceitainly lower than foi- Perth, though in several cases within 20' 
miles of that j)oint. the evidence points to an 0 ])tiimim for 7 y 
hiheniali.s lower than those for P. citrophtUom and terrcsirh 
which are given by Fawcett (14) as 20. oo and 31. 5o resj)ectively. 
l\k)mz da Maia has also noted (20) the relation of the disease in 
J’ortugal to low tcmijteraturos. 
-Vs |)ojiited out already cultures have failed to survive at room 
temj'erature in Ihn-th during the summer necessitating their storage 
"1 f place. Sub-culturing during the summer has been inisC- 
ble only !>y kee].ing the cultures at reduced temperatures. Two 
attempts to forward cultures, to Dr. F. J. Butler, at Kew. faihMl. A 
^■^niIar failure resulted when Dr. Butler forwarded a culture isolated 
hy him in 1924 from orange shiinnents in London fnmi Western 
Australia. A culture forwarded to Mr. Mb Waterhouse, at Svdnev. 
<tmd durmg the summer, and I have since heard from Dr. Buthw- 
that Ins isolation had come to the same end. Cultures of P. vitro- 
