Disease of Olive and Orange Trees. By W. G. Farlow. 113 
have not been able to see that they enter into the cells of the 
stellate hairs or epiclermis and act like haustoria. The surface 
of the hairs and epidermis, however, seems covered with a sticky 
substance (of which we shall have more to say hereafter), to which 
the hyphae closely adhere. Plate CL., Fig. 2, shows one of the 
stellate hairs seen from below, with a portion of the mycelium 
growing upon it. 
Various modifications of the mycelium are found principally 
on that portion growing on the outer part of the stellate hairs 
exposed to the air. After reaching a certain stage of development, 
they grow together in such a way that the hyphse coming together 
laterally form a sort of membrane, as shown in Plate CL., Fig. 1, d. 
This membrane is composed of only one thickness of cells, but is 
very uneven as it follows and conforms to the inequalities of the 
hairs. Its general direction is parallel to the surface of the leaf or 
stem on which it is found. 
Conidia. — The hyphse at their free ends branch in all direc- 
tions, and bear reproductive bodies of several kinds. The simplest 
form is that shown in Plate CL., Fig. 8, d, where the ordinary cells 
of the mycelium divide by cross partitions into two parts, which 
do not respectively grow to the same shape as the mother cell, but 
remain together two by two, as shown in the figure ; the hypha 
becoming zigzag by the alternate lateral displacement of the pairs 
of cells, which finally drop oft' and readily germinate, each cell 
producing a germinal tube. In other parts of the mycelium, the 
terminal cell of certain threads divides by means of partitions, 
parallel to and at right angles to the axis of the filament, until a 
compound body is formed, which resembles the spores of the so- 
called genus Macrosporium. These bodies, which can only be 
described as irregular conglomerations of cells of an oval outline, 
are produced in great abundance and average '015 mm, by '025 
mm., but are often much larger, though often smaller. They easily 
drop from their attachments and germinate, each cell being 
capable of producing a germinal tube. Other hyphae, rising at 
right angles to the plane of the membranous portion of the 
mycehum, grow more and more attenuated, and branch at the tip ; 
the terminal cells divide in two, as in Plate CL., Fig. 3, c, fall from 
their attachment, and germinate. This last modification of the 
hyphse, which is by no means so common as the two previously 
described, will be recognized as corresponding to the so-called 
genus Helminthosporium, or Cladosporium, if we examine before 
the terminal cells have divided. It is out of the question to give 
specific names to such forms as those just described, which, since 
the publication of Tulasne's ' Carpologia Fungorum,' are known 
to be dift'erent states of development of species of Pyrenomycetes. 
Pycnidia. — Besides the forms already described, there are 
