a Pitti ey Ph ysiolagical Botany. 
lie ripe fruits fall off and are worthless, Ehe,, cause ne 
the disease is a Fungus, Axvascus Pruni. | ae ae 
The fotato-disease makes its appearance first on the a 
green parts of the plant, forming 
brown spots on the leaves and 
stems, usually in July and August. 
A short time afterwards the tu- 
bers are found to be diseased,and © 
begin to decay. The decompo-. .— 
sition is either moist and of a 
disagreeable odour, or ends in _ 
a drying up of the tissue; the ~~ + 
former kind being generally de- 
scribed as the true potato-disease, 
although the two forms pass into— 
one another. It is only rarely 
that the decay of the tubers pre- 
cedes the sickening of the plant 
itself. The parasite which causes 
this disease is also a’ Fungus, 
Peronospora infestans. It pene- 
trates the tissue of the leaf, its 
conidia-bearing filaments pro-- — 
jecting through the stomata. | © 
The tissue of the leaf dies under | — 
its influence, and the tubers © 
which are subsequently attacked 
also decay (Fig. 377). ie 
Pete inetis-Alaments. frei The true potato-disease’ broke out 
a rotten potato, fogether with 
the spherical spores y called 
Otdium violaceum, and the long- 
about the year 1830, and spread with — 
terrible rapidity during the next ten | 
ish multicellular spores z «f years ; and has never since entirely dis- 
Husisporium Solini; young f 5 d ‘i ; oo 
plants are germinating from both appeared. Its study suggested a variety ~ a 
forms. (This fungus very com- of causes: among the rest damp wea- (4 
monly accompanies, but is not : ge) 
the cause of, the disease. x 400.) ther, too strong manuring and the ry 
cutting up of the ‘ seed- ‘patna ‘ ee 
o | 
A peculiar disease, also caused by a Fungus, but which Be 
‘ j a. aia 
‘ P pre of ee 
é va 4 ig 
ps ee LA RS 
* ‘ “f) re fy © iN 
24 1 ott OP es Stl, 
