TREE RooT DISEASES. Il 

The mycelium first attacks and kills the youngest rootlets, 
and then enters into the larger branches of the root, in which 
it rapidly spreads and forms an irregular network of slender 
strands ; finally bursting through the cortex and enveloping 
the roots in a snow-white, fluffy mycelium, here and there 
running into slender, cord like strands, which traverse the 
soil, and by this means spreads from one tree to another. 
Ata later stage of development, numerous minute, black 
compact masses of mycelium or sclerotia are formed in the 
cortex of the roots, and from each of these spring several 
slender spines, each of which bears an abundant crop of 
conidia or reproductive bodies at its tip. In addition to the 
white mycelium, a very characteristic pale brown or olive 
mycelium is also present on the surface of the roots, formed 
of septate or jointed threads of variable thickness, having pear- 
shaped swellings at intervals; these swollen portions finally 
become free by the disappearance of the intermediate por- 
tions of the mycelium, and form bodies capable of germinating 
and giving origin to a new crop of mycelium. Under certain 
conditions some of the sclerotia, instead of producing the 
spine-like bodies bearing conidia, become converted intc 
hollow spheres or pycnidia, containing in their interior 
numerous minute reproductive bodies or stylospores which 
germinate at once and produce new plants. Finally, the 
highest, or ascigerous form of fruit is rare, and only develops 
‘on old trunks that have been dead and decayed for a long time. 
Up to the present the last mentioned form of fruit has only 
been met with in France, and its structure is such that the 
fungus proves to belong to the Zwécracez or truffle family. 
Dematophora necatrix is almost entirely confined to heavy 
clay soils, where the water drains away with difficulty, 
whereas Dematophora glomerata, Viala, an allied, but much 
rarer fungus, with a similar destructive habit, hitherto 
observed only in France, is met with attacking plants grow- 
ing in loose sandy soil, where the subsoil is wet. 
During the spring of the present year (1896) a sample of 
soil was received by the Royal Horticultural Society from 
Mr. Hooper, Cambridge, Waikato, New Zealand, containing 
roots of apple trees attacked by a fungus, with a communi- 
