

1l 
disease, because many of the pate oom be washed off by the rain on 
to the earth where they cannot germ 
Secondly, the power of germination ‘of the Spores is not retained 
indefinitely. After a certain time the spores die if they have not found 
the conditions favourable to their development. The length of time 
during which they retain their vitality varies according to the cireum- 
stances ; if dried up, they would die in a day or two, but if the weather 
were moist they would probably retain their germinating powers some 
weeks. But as far as is at present known they do not retain their 
Mraz beyond the summer in which Pa are matured. They would 
not last over from one season to another 
irdly, in connexion with témoi measures, it should be noticed 
that the spores when ripe and whilst germinating are outside the leaf, 
and have not entered into that intimate connexion with the tissues of 
leaf of the onion plant which is characteristic of the mature fungus. 
It has been Sorte above that the spores of the fungus do not retain 
their vitality from one season to another, and it is obvious that the 
length of life of the mature fungus is limited sl that of the onion upon 
which it lives. Hence there must be some means by which the fungus 
is enabled to last over the autumn <i winter pat the young onions 
of the new crop are ready to afford it a new home. This is effected by 
means of ae cells, termed Eiaa es, which are formed in the 
followin 
Certain ‘of the tubular root-like processes which form the meshwork 
inside the tissue of the leaf swell up at their ends. Thus a knob is 
formed full of living matter, and this is cut off from the contents of the 
rest of the fungus by the formation of a transverse partition. In the 
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ar) 
the latter (Fig. 
surrounds itself fi a very thick wall or coat, and is now terme 
ae (Fig. 9 
large number of these resting-spores are formed, so that in 
a ton of an onion leaf, which has been diseased for some time, a 
ary number of these, each aeree bya at -i ick coat, are fore ed. 
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thick wall which encases them. 
When a field of onions has been destroyed by the Onion a the 
withered leaves are crammed with resting-spores. e leaves fall to 
the ground, mabi ot. with them thousands of Da little Se any one 
i as 
o a suitable home. Then with the first met warm day oe begin 
to germinate, and soon the new crop of o s falls a victim to the 
fungus, produced from resting-spores itch 3 were themselves produced 
from the fungus of the preceding crop. 
b. Sexual. 
