MILDEW AND BRAND. 
181 
say, an indefinite number of points in the vicinity of the 
future mycelium developed threads ; and these, in the process 
of growth, interlaced each other, and ultimately, by means of 
transverse processes, became united into one vegetative system, 
in which the individuality of each of the elementary threads 
became absorbed, and by one combined effort a spore-spot, or 
cluster of fruit, is produced. In the first instance a number 
of minute, transparent, colourless cellules are developed from 
the mycelium : these enlarge, become filled with an orange- 
coloured endochrome, and appear beneath the cuticle of the 
leaf as yellowish spots. As a consequence of this increase in 
bulk, the cuticle becomes distended in the form of a pustule 
over the yellow cellules, and at length, unable longer to with- 
stand the pressure from beneath, ruptures in an irregular more 
or less elongated fissure (as in fig. 24), and the yellow bodies, 
now termed spores (whether correctly so, we do not at present 
inquire), break from their short pedicels and escape, to the 
naked eye presenting the appearance of an orange or rust- 
coloured powder. In this stage the spores are globose, or 
nearly so, and consist of but one cell (resembling figs. 3, 6, and 
9). It will afford much instructive amusement to examine one 
of these ruptured pustules as an opaque object under a low 
power, and afterwards the spores may be viewed with a higher 
power as a transparent object. The difference in depth of tint, 
the nearly colourless and smaller immature spores, and the 
tendency in some of the fully matured ones to elongate, are all 
facts worthy of notice, as will be seen hereafter. 
A month or two later in the season, and we will make 
another trip to the cornfield. Rusty leaves, and leaf-sheaths, 
have become even more common than before. A little careful 
examination, and, here and there, we shall find a leaf or two 
with decidedly brown pustules intermixed with the rusty ones, 
or, as we have observed several times during the past autumn, 
the pustules towards the base of the leaf orange, and those 
towards the apex reddish brown. If we remove from the 
browner spots a little of the powder, by means of a sharp- 
pointed knife, and place it in a drop of water or alcohol on a 
glass slide, and after covering with a square of thin glass, sub- 
mit it to examination under a quarter-inch objective, a different 
series of forms will be observed. There will still be a pro- 
portion of sub-globose, one-celled, yellow spores ; but the 
majority will be elongated, most with pedicels or stalks, if they 
have been carefully removed from the leaf, and either decidedly 
two-celled, or with an evident tendency to become so. The 
two cells are separated by a partition or dissepiment which 
divides the original cell transversely into an upper and lower 
cell, with an external constriction in the plane of the dissepi- 
