CHAPTER VII. PHENOMENA OF VEGETATION. PARASITES. 383 



prothallia of Ferns and quickly kills them, while P. megalacanthum was only 

 rarely induced to penetrate into them, and its development in them was slow. 



Nectria cinnabarina 1 is one of the most common saprophytes on dead twigs. 

 Their bright red cushions burst forth in abundance from the rind of branches which 

 have been killed by frost in the previous winter. Their germ-tubes do not attack the 

 surface of living branches, or living rind or bast tissue when laid bare. But if 

 they find their way to a wounded surface where the wood is exposed, they penetrate 

 into it, and the mycelium grows rapidly upwards in the vessels, causing decomposi- 

 tion of the wood-substance ; this is followed by the death of larger or smaller portions 

 of a branch or stem, and the further development and the formation of perithecia 

 by the Fungus then takes place in the dead rind. This at least is the course of 

 proceeding in Acer, Tilia, and Aesculus. Other woods gave an uncertain or negative 

 result. 



Nectria Cucurbitula, Fr. 2 developes a mycelium producing gonidia when raised 

 from spores in a nutrient solution. It is uncertain whether this species can arrive at 

 the formation of perithecia in this saprophytic mode of life. But its germ-tubes 

 penetrate through wounds in the living rind of pines into the living tissue, and spread 

 rapidly through it during successive periods of vegetation, covering a distance of 

 10 cm. in the longitudinal direction in one season; they at last kill the tissues 

 which they have attacked and then form perithecia which come out upon the surface. 

 This highly pernicious Fungus usually makes its attack where wounds have been 

 caused by hail-stones or by fractures under a weight of snow, and especially where 

 the bark has been eaten away by Grapholitha pactolana. 



Nectria ditissima, Tul., the Fungus which causes canker in deciduous trees 

 especially in the apple-tree 3 , agrees closely with N. Cucurbitula as regards the arrange- 

 ments which have been described. The Fungus penetrates at some injured spot into 

 the living rind and spreads slowly in it and also in the adjoining wood ; the parts 

 attacked are dried up and destroyed so far as they consist of juicy tissue, while 

 cushion-like formations appear all round them advancing centrifugally in successive 

 periods of vegetation ; in consequence of these and of the successive partial drying up 

 of the parts, malformations are produced in the shape of swollen places with a 

 depressed dead centre, which themselves also in course of time partially die away. 

 Gonidia and perithecia emerge from the periderm at the margin of these swollen 

 places where the tissue is still succulent. 



The wood-destroying Hymenomycetes occupy a prominent position among 

 facultative parasites. Agaricus melleus may be taken first as a typical example of this 

 group. We know from Hartig's researches supplemented by Brefeld that the spores 

 of this plant germinate on dead vegetable substances and produce the mycelium which 

 is characterised by its strands or rhizomorphous form. This mycelium may 

 develope spontaneously as a saprophyte and bear sporophores in and on dead wood, 



1 H. Mayr, Ueber d. Parasitismus v. Nectria cinnabarina (Unters. a. d. Forstbot. Instil, z. 

 Miinchen, III). 



a R. Hartig, Unters. a. d. Forstbot. Instit. z. Munchen, I, p. 88. 



3 R. Hartig, 1. c. I, 109. R. Gothe in Thiel's Landw. Jahrb. IX (1880), p. 837. 



