592 
slightly translucent, portions of which were held over the flame of a spirit- 
lamp, when instant resinous ignition took place. Its smoke had the odor 
of burning shellac. The “rust,” so called, proved to be composed of 
albuminous and resinous matter combined with vegetable cellular tissue, 
earthy matter, &c., unimportant to consider in this case. My atten- 
tion was next directed to the investigation of the black matter on 
the leaves, branches, and fruit. I removed a portion of the black mat- 
ter from a leaf. It appeared as if composed of black, granular matter, 
cemented with flour-paste, and formed into thin sheets of the thickness 
of tissue-paper. When dried it may be cut to any form desired. Some- 
times it appears as a fine black powder scattered over the leaf, and is 
frequently found in quantity at the base of orange-buds. On placing a 
portion of the black matter under a power of about 100 diameters, it is 
seen to consist of a branched and jointed mycelium or spawn of a fun- 
gus. After making many observations, under a power of about 600 
diameters, the fungus, in its various stages, was clearly defined. [, 
Fig. 1, represents its mycelium growth; 2 2 its budding cells, which 
terminate in fruit-cells; see 3, 3, 3, 3, bearing spores which germinate ; 
44 are fungoid aggregations which throw out filaments; their relation 
to the black mycelium is not represented thus far; 5 represents what 
appears to be a cross-section of the asci or fruit, when perfectly formed 
and cut through its greatest diameter crosswise. The surface of the 
leaf is generally covered with these germinating-spores when the black 
mycelium is on the leaf; being colorless they are invisible. Frequently 
Vandyke colored cells are seen on the leaf. They consist of disjointed 
mycelium. To the naked eye the fungoid spores, &c., appear black, but 
under the microscope they appear of a Vandyke brown, with the excep- 
tions noted. It is known to mycologists as black mycelium. Berkley 
says that of late years the black mildews have raged to such an extent 
in the Azores and Ceylon as to threaten the complete annihilation of the 
orange and coffee plantations, and the ravages have been scarcely less 
among the olives in some parts of Europe. It is impossible that light 
can have its proper effect through such a medium on the tissues 
of the leaves. It would be as rational to expect that plants would 
thrive under a brown bell-glass as that vegetation should not be im- 
paired when the greater part of the plant is covered with a thick, dark 
felt. The mildews are often accompanied or preceded by a coccus, and 
I believe that the first stage of growth of most Antennarie is more fre- 
quently observed where the leaves have been soiled with honey-dew.* 
It has long been observed that a black powdery substance always 
forms on the leaves, buds, and the fruit of the orange-tree and some 
other plants when attacked by the “ mealy-bug ” and orange-scale in- 
sects. The plants are doubtless punctured by these pests, causing a flow 
of sap from the ruptured parts, which probably forms a nidus for the 
black mycelium to vegetate in, spreading over the whole tree, blacken- 
ing and destroying it. The skin or epidermis has its peculiar functions 
to perform, and, if covered, its healthy action will be impeded. All 
molds and blights are plants of a very low organization, and live in this 
predacious way ; but many are flowering herbs, and even shrubs. One of 
the latter is the mistletoe, the seed of which germinates on the boughs 
of the tree where it falls, or is lett by birds, and forming roots, which 
penetrate the bark, the plant ingrafts itself into the wood, to which it 
* Honey-dew is a sweet, saccharine substance found on the leaves of trees and other 
plants in small drops like dew. Two substances have been called by this name, one 
secreted from the plants, and the other deposited by a small insect. 
