INJURIES INDUCED BY PLANTS 83 



tributed throughout France, Italy, Switzerland, Austria, and 

 south-west Germany. 



Amongst the root-diseases of the vine, that which is caused 

 by Phylloxera vastatrix is generally known. Very similar 

 pathological symptoms occur on the stems of plants that are 

 attacked by the vine-root fungus, and confusion often enough 

 results. 



Whether Agaricus melleus also is injurious to the vine as has 

 been maintained I am not in a position to say, because, so far, 

 no specimens have been forwarded to me in which the fungus 

 could actually be identified. On the other hand, it appears as 

 though, in very wet years and on heavy ground, "root-rot" may 

 arise as a result of asphyxia that is to say, owing to deficiency 

 of air in the soil. On such suffocated vines a fungus, Roesleria 

 hypogcea, often occurs, which, it appears to me, is most probably 

 saprophytic in character. 



The parasite that we are here discussing spreads in the vine- 

 yards from plant to plant by means of its underground mycelium, 

 so that we often hear of great damage being done. Other plants 

 that are cultivated in the vineyards, such as fruit-trees, potatoes, 

 beans, beet, and the like, also fall a victim to the fungus. During 

 my investigations I found that the mycelium could at once kill 

 young maples, oaks, beeches, pines, spruces, &c. 



On plants where the mycelium is vigorously developed, as in the 

 case of the vine, Fig. 29, and the young maple, Fig. 30, it forms 

 a luxuriant snow-white mass of a woolly or strand-like texture, 

 which adheres to the outside of the plants, though it may also 

 spread in the ground to long distances. Where this mycelium en- 

 counters the fine fibrous roots of other plants, it kills them, and, 

 at their base, bores into the interior of the larger roots, Fig. 3 1 a, 

 spreading afterwards in their interior in the form of peculiar 

 rhizomorphs, Fig. 32, and killing all the adjoining tissues. In 

 the soft cortical tissues of the vine-root they retain their strand- 

 like appearance, and by ramifying laterally and outwards they 

 envelop the root in a network of strands, Fig. 33. 



In structure these rhizomorphs are entirely different from those 

 of Agaricus melleus. In Fig. 34 I have represented somewhat 

 diagrammatically the apex of one of these rhizomorphs, and refer 

 for details to the description appended to the illustration. 



G 2 



