W. G. Farlow—Disease of Olive and Orange Trees. 39 
to the Hrysiphei. Occasionally there are little knob-like pro- 
jections of the cells which seem to indicate haustoria; but, by 
the most careful examination which we have been able to make, 
we have not been able to see that they enter into the cells of 
the stellate hairs or epidermis and act like haustoria. The sur- 
face of the hairs and epidermis, however, seems covered with a 
sticky substance (of which we shall have more to say hereafter), 
to which the hyphe closely adhere. Plate 3, 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 mee of develop- 
ment, they grow together in such a way that the hyphae coming 
together laterally form a sort of membrane, as shown in Plate 8, 
ig. 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. 
, Voniwa.—The hyphe, at their free ends, branch in all direc- 
tions, and bear reproductive bodies of several kinds. The sim- 
plest form is that shown in Plate 8, Fig. 3, 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 displace- 
ment of the pairs of cells, which finally drop off and readily 
germinate, each cell producing a germinal tube. In other parts 
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 resem- 
bles the spores of the so-called genus Macrosporium. These 
bodies, which can only be described as irregular conglomera- 
tons of cells of an outa) Onli 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 hyphe, rising at right angles to the plane of the 
membranous portion of the mycelium, grow more and more 
attenuated, and branch at the tip; the terminal cells divide in 
two, as in Plate 8, Fig. 8, ¢, fall from their attachment, and 
germinate. This last modification of the ee which is by 
no means so common as the two previously described, will be 
recognized as corresponding to the so-called genus Helminthos- 
cells have dvidaa. It is out of the question to give specific 
names to such forms as those just described, which, since the 
