CHAPTER VII. PHENOMENA OF VEGETATION. PARASITES. 381 



substances, and even according to Brefeld on bread. If the 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 1 . 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 (i882\ p. 1368. 



