448 SECTIONAL TRANSACTIONS.—K. 
Phytophthora Porri has been found to be the cause. The main source 
of this disease is the contaminated soil ; the ploughing in of diseased leeks 
is thus deleterious. The fungus enters by the leaf and proceeds down the 
stem. Onions and Allium fistulosum are immune. ‘The resistance of certain 
parts of the host plant is associated with the method of entry of the fungus. 
Susceptibility varies with the age of the plant, resistance being highest at the 
seedling stage. ‘This disease may be compared with certain diseases of 
the onion where resistance is associated with the presence of a special 
chemical in certain tissues. Control of this disease is not practicable by 
means of spraying. Selection for resistance and crossing for immunity is 
promising. ‘Trials of interspecific crossings using Allium species are in hand, 
to see if immunity can be transferred to the commercial leek. 
Mr. A. R. Witson.—The relation of Botrytis to the ‘ chocolate spot’ 
disease of beans (Vicia Faba) (3.20). 
“ Chocolate spot ’ disease of Vicia Faba is characterised by the appearance 
of chocolate brown lesions on the shoots. The disease has been attributed 
by various authors to different causes. These are summarised as follows : 
Paine and Lacey (1923), Bacillus Lathyri; Riker and Riker (1932), unnamed 
bacteria ; Magee (1933), exudate of Aphis rumicis; Ikata (1933), Botrytis 
Fabe \kata. Research carried on during 1931-35 at Cambridge has shown 
that ‘ chocolate spot’ lesions may be due to various causes, chief among 
which is infection by Botrytis spp. The original inoculum comes from 
rotting debris on the ground and later from leaves which have been killed 
by the first attack. ‘There are two definite types of infection, ‘ unlimited ’ 
resulting in extensive blackening and death of the shoots and ‘ limited ’ 
resulting in true ‘ chocolate spot.’ ‘This latter type does not often seriously 
damage the plants unless environmental conditions remain favourable to 
the growth of the fungus. Other factors, however, determine to a large 
extent the severity of the outbreak, such as soil deficiency in lime, potash, 
etc., poor drainage and frost. Poor growth resulting from one or more of 
these causes predisposes the crop to severe attack should suitable environ- 
mental conditions arise. 
Mr. C. G. Dosss.—The life history of Dicranophora fulva (3.50). 
This member of the Mucorales possesses sporangioles containing large 
reniform spores, as well as sporangia of the Mucor type. Studies of the 
sporangial stage confirm the presence of a columella in the sporangiole, a 
distinction from Thamnidium which has been denied by Vuillemin, and 
further show that the sporangioles grade into the large sporangia by inter- 
mediate forms. ‘he columella, which is spherical, not conical as pre- 
viously reported, sometimes branches and may give rise to the two short 
points from which the genus is named. The range in spore size (5-50 L) 
is extraordinarily wide, and occasionally a sporangium may liberate its 
contents as a single spore. 
The remarkably heterogamic sexual stage has been further elucidated. 
The lobed female hypha, about 60 uw in diameter, which may form a branch 
system up to 1 mm. long, forms zygospores wherever it comes in contact 
with a male hypha. Passage of contents from the male to the female 
gametangium has been observed. ‘The fungus is remarkably sensitive to 
light, very short illumination being sufficient to inhibit the development of 
the sex organs, and to induce the formation of sporangia, which are not 
produced in the dark. 
