CHAPTER VII. —PHENOMENA OF VEGETATION.—PARASITES. 3 81 
substances, and even according to Brefeld on bread. Ifthe spores for example are sown 
on a piece of carrot which has been killed by hot water, a vigorous fungal growth 
is obtained ; but on the moist surface of living portions of the same plant only short 
germ-tubes are produced, as in simple water, and these do not penetrate into the living 
tissue, even where the surface has been injured ; the parts which have been sown 
remain for weeks free from the Fungus. If on the contrary the infection of the sound 
part is due to germ-tubes which have developed to a small amount only in a nutrient 
solution—how much cannot be exactly stated, but it is sufficient if the germ tubes are 
scarcely visible to the naked eye,—they penetrate at once into the living tissue and kill 
it, and form mycelium and sclerotia; pieces of older mycelium behave in the same way. 
The results are obtained with all parts of the plant, according as they are alive or dead 
and are inoculated with spores or with germ-tubes which have reached a certain stage 
of development. I never saw a germ-tube make its way into living tissue without 
having been previously nourished as a saprophyte; some statements to the contrary 
will be noticed in the sequel. 
But Sclerotinia Sclerotiorum is also found as a parasite on living cultivated plants, not 
to mention the injury which it does to turnips in store. I observed it destroy the beans 
(varieties of Phaseolus vulgaris) in a garden in the neighbourhood of Bregenz two years 
successively, and a similar occurrence has been reported recently by Prillieux from 
Algeria’. It is also very fond of attacking Zinnia elegans and the Petunias. If we try 
to infect sound specimens of these favourite species, even quite young seedlings, with 
spores which are germinating in pure water, we always get the same negative result as 
in the carrot; the plants remain uninjured. If an extremely small amount of some 
nutrient solution is supplied to the germ-tubes emitted by the spores they at once 
become strong enough to penetrate into the plants at any place and then to develope into 
a mycelium which will spread through them and destroy them and form sclerotia, unless 
the amount of food which it obtains is insufficient, as in the case of seedlings. The 
same results were obtained with older vigorous mycelia. In the case of plants growing 
naturally and rooted in the soil we can see how the Fungus as a rule makes its way 
into the stem from the surface of the ground, and leaving the roots untouched ascends 
in the tissue of the aerial parts, especially in the masses of parenchyma. In this way 
the whole plant is killed and dried up and becomes of a pale straw colour. During this 
process it is not necessary for the Fungus to appear on the surface ; in fact it often re- 
mains quite inside and then forms its sclerotia in the shape of cylindrical or prismatic 
bodies inside the dead pith especially in the neighbourhood of the nodes, or, as in 
Phaseolus, in the fruits also between the ovules ; in Zinnia it often fills the receptacle with 
a sclerotium which like it is conical in shape. In a very moist environment however the 
mycelium may come out to the surface of the plant which it has attacked in smaller or 
larger quantity in white flakes and tufts, and can also form its sclerotia there ; it may 
also pass over to the foliage of neighbouring plants with which it comes into contact, 
and destroy them, proceeding from above downwards. This may be observed in a very 
striking manner where beans stand close together in a plot. 
All these phenomena may easily be reproduced by artificial cultivation in pots. It is 
only necessary to place some mycelium, grown from spores and made capable of infec- 
tion in the way described above, at the base of the plant to be infected, and keep the 
whole sufficiently moist. Experiments have shown that commencements of mycelia 
capable of infecting other plants may be obtained from spores on a small bit of dead 
vegetable substance, a piece for instance of a dead leaf. The mycelia therefore may be 
formed on every bit of moist ground covered with vegetation to which the spores find 
their way. Sporocarps formed spontaneously from sclerotia of the previous year were 
.to be found in the bean-garden just spoken of, and these supplied the spores. 
As a saprophyte the Fungus developes on all dead parts of plants employed in 

1 Comptes rend. 99 (1882), p. 1368, 
