m 
From the statements made it will be gathered that infection can 
only take place through the tuber. This can be effected in two 
ways ; from a previously diseased tuber that has been used as a 
" a .■[." or from conidia present in the ground. The latter method 
1 1 wth of a diseased crop on the same land. In 
either rase when a tuber once conta uivceliuni 
<>r tin fungus, the probabi iry is - is offs >i >u \< ill 1 e infected 
r , ' , i ,r ;i11 r ''ne. fhe mycelium passing from one generation to another. 
This statement however is not absolute. Last war in hers obtained 
Irum potatoes badly affected with ■• leuf-ourl " were planted in the 
experimental ground adjoining the Jodrell Laboratory at Kew, 
and every plant showed the disease in every part. The 
tubers produced by this crop were planted again this rear, and 
;'">"'- "'ver plant is obvioush d seas d, on. root U .'ring fo.u 
- 
■ liy. Another root vriil, thv haulms has two diseased, 
ung three healthy. All the other plants are diseased 
• The probable explanation of this is that for some 
-.n. the mycelium present in the ruber did not pass 
up into the shoots that remained free from disease. 
The blackish patches that appear on diseased leaves and haulms 
Lrely of conidia or reproductive bodies of the fungus, 
-.nate from the dense weft of mycelium pres,nt in ihe 
red, and when mature are divided into several cells by 
i to each other. When 
germinate readilv during any 
be year, provided the requisite conditions are present. 
o nature, however, it so happens that such co.lli.i.Mis 
:it all seasons, but only during that period 
I;;--- n;-c,^ry for the vigorous germing ofconidia an, 
.' ^ / ' '■',' -' - ■ ■ ■ , .:- ', ...;..- ,. 
nimum or lowest temperature at 
•,, ,.ir (1( ., ;',. ! .'■ , l i . r i .' #I1 "^ rD 4^ a ^ m m a . ma nner suflieiontly vigorous 
ie dead 1< 
until the following season.' The" 
'eiatttre for germination is G4° F ~ The 
empiTuture for healthv germination is 7 
1 i l:l!l(,!1 j« flu' optimum temperature of G4r 
verv lono U m„°l ^T 1111 temperature. 
i t-\ ' [ germ-tubes ar. 
J 8 numerous secondary con 
*■'* mdan conidia ar • 
'!., ifi ■ " 7 r!u --" 1 '^ Alter naria ' In 
• the food becomes exh 
oh h^I bes conc entrate at intervals 
