Reproduction, 
a, Asexual. 
Germination. 
10 
As this network of roots grows and spreads through the tissue, some 
of its tubular branches force their way into the tee of a 
stoma, and pass out ia it into the air, Fig. 4. The young 
stem ‘thus formed now commences to fork or branch, as is indicated in 
Fig. 5, The bra Aeng again ous and kree small portions 
of their ii are constricted off and form the spores before mentioned, 
t has been stated that the number of Somită apin the nion leaf is 
roughly about 70,000 to the square inch. If the onion is badly diseased 
one of the branching stems of the fungus will be found projecting into the 
air through about one stoma in every ten. In some cases two (Fig. 3) 
and even three (Fig. 4) stems may emerge from one stoma, so thation 
a square inch of a diseased onion leaf we may fairly estimate the 
number of stems of the fungus as almost one-tenth of the number of 
stomata, that is 7,000. If we take 20 as the average number of spores 
one stem, and that is aie, below ae above oe averages we Sanl 
sin onion ay the 
number of (20 x 7,000) 1 a 000 pain canis capable mi tereo idag the 
fungus, and hence the disea 
There are two methods 6 which the onion fungus donna dete itself : 
a, the asexual; 6, the sexual. The asexual method of reproduction is 
effected by means of the above-mentioned spores. Each spore is an 
exceedingly minute sac or bag containing living matter; the shape is 
oval and rather more pointed at Hi end attached to the branch than at 
the other. It has a slight violet 
These spores are, from their nines size and eS easily blown 
about by the wind, and float through the air, and it y this means, 
and iss by means of insects flying rom one onion fie d to the next, 
that the spores are carried about and the disease spread over a field, 
and from one field to another. 
n one of the spores falls upon an onion leaf it will, providing 
corian external conditions are present, begin to germinate. These 
external conditions, which are necessary to the germination of the spore, 
are, tk certain degree of warmth, and, secondly, a certain degree 
of moisture, acomniditions which, unfortunately, are seldom wanting in 
ie ae a, 
spore germinates upon the leaf of an onion it puts forth a 
long pubulär outgrowth, Fig. 6, which makes its way to the nearest 
i 
turn of reproducing the fungus. 
With respect to the germination of these spores and the em 
spread of the disease, two or three points are worthy of comment 
rm, humid weather 
disease spreads with a rapidity which is e aly i intelligible when the 
normous number of spores is taken into account. Sharp showers of 
bin followed by sunshine will also tend to arrest the ordi of the 
