440 
Williamson .— The Origin of ‘Golden ’ Oak. 
the fact that the coarse of the hyphae is generally vertical in the wood, so 
that islands of vessels and tissue containing hyphae would occur. 
Tests for tannin show that many of these cells contain some ‘ tannin 
body’ as well as the refractive substance, often masking the yellow colour. 
It is possible to dissolve out the tannin and obtain cells still showing yellow 
or tangerine-coloured contents. 
These bodies agree, in certain reactions, with the behaviour of the 
material known as ‘ wood-gum ’. They are insoluble in water, alcohol, 
ammonia, chloroform, acetic acid, concentrated nitric, hydrochloric, and 
sulphuric acids. In most of these cases tannin is dissolved out and the 
refractive substance, yellow, light orange, or red-brown, remains. Strong 
potash dissolves some of the cell contents, leaving pale yellow or tangerine- 
coloured substances in the medullary rays and some patches of cells. 
Whether this ‘ tannin so often present along with the yellow substances, is 
the same as the ‘ tannin ’ in uninfected oak it is impossible to say with the 
micro-chemical tests available. 
The yellow colour of the wood may be due to two factors, the yellow 
substance exuded by the fungus and the yellow colour of the conidia. 
Colour may be produced in wood by fungi due to the colour of the mycelium, 
such as certain species of Graphium may produce on oak, pine, &c. Other 
cases have been recorded in which the fungus exudes a soluble pigment 
which, according to Hedgecock ( 3 ), is absorbed by the lignified cell-walls so 
that the wood is actually stained. Hedgecock describes Penicillium aureum 
which may produce a yellow colour in oak. This fungus exudes a soluble 
pigment in the form of granules and also possesses a mycelium, which may 
have swollen cells and bear conidiophores, consisting of a whorl of branch 
hyphae bearing sterigmata and long chains of oval conidia. The points of 
difference between this fungus and Eidamia catenidctta are as follows : 
(i) P. aureum is dimorphous, having a mycelium with grey-green 
coloured fruiting clusters and also a sterile mycelium which can be lemon- 
colour or orange-red according to the acidity or alkalinity of the medium. 
E. catenulata has a colourless mycelium and its fruiting clusters are yellow. 
(2) The swollen cells in the mycelium of P. aureum have no thick walls and 
do not separate from the hyphae, so cannot be compared with the hyaline 
spores of E. catenulata. (3) The conidia in P. aureum are 3—4 /x by 1-5-2 u 
and contain a blue-green pigment which is soluble in hot alcohol, whereas 
those of E. catenulata measure 4-7 /x by 2-3-5 and possess a yellow colour 
insoluble in alcohol, &c. (4) The yellow pigment exuded by the hyphae of 
P. aureum is soluble in slightly acid or alkaline water, hot alcohol, &c., and 
is absorbed by the lignified cell-walls. In E. catenulata the hyphae exude 
a yellow substance which is insoluble in acid or alkali ; and is stored in the 
cell cavities as a refractive yellow or orange ‘gum \ and there is no staining 
of the cell-walls. 
