186 THE NORTHERN MICROSCOPIST. 
which I have described, or to make osmosis, from such a place 
upon the shell move the diatom in the direction of its length. The 
assumed presence or absence of a gelatinous film enveloping the 
diatom does not materially vary the conditions of the problem in 
either case. If we assume that the osmotic action is at the ex- 
tremities of the shell, the observed phenomena, as to the action 
upon the gelatinous mass when in the middle of the frustule, are 
unaccounted for. 
As to the manner in which the lapping of the halves of the frus- 
tule along the raphe is effected, it may be most easily seen in some 
of the coarser Pleurosigmas. In broken shells of P. attenuatum 
and P. formosum I have seen it very plainly demonstrated. Some- 
times the thickened line of silex, which borders one-half of the 
frustule, will be found sticking out alone, the thinner part of the 
shell being broken away from it. Sometimes it will be in its nor- 
mal position, but the lateral halves of the shell will be separated 
by pressure so as to show on one side the thick edge, and on the 
other the fitting gutter caused by the projection of a thin lip. 
Occasionally also a cross fracture of the shell will be found on a 
broken fragment, in such position that we get the benefit of a 
cross-section, and see the whole joint in the form I have described. 
—American Monthly Microscopical Journal. 
LEAF FUNGIVIN AUGUS® 
[HE Microscopist who takes an interest in leaf fungi will find 
August especially favourable for his purpose, for a large 
number of the most interesting of such parasites now begin to 
make their appearance, while others, to which I refer, placed in 
favourable situations, may have made their appearance even earlier. 
Amongst them are the Erysiphe, a section of the Perisporiacei. 
Lrysiphe Linkit, the Mugwort blight (on Artemisia vulgaris) may 
be found in great plenty in this month. I have often met with it 
on the river bank near Cheadle Bridge ; in the neighbourhood of 
Northenden; near Southport, and elsewhere. The appendages 
surrounding the fungus and the sporangia with its two spores are 
very interesting features of the plant. 
Lrysiphe Marti, Pea blight is common on many plants besides 
peas ; it is also on beans, on Umbellifera of various species, and 
other plants. This fungus is very abundant in autumn, especially 
after a wet period. ‘The sporangia and appendages differ from Z. 
Linkit, and will soon be known by comparison. 
Lrysiphe graminis. Grass blight is not so common as the above, 
* 
