STRUCTURE. 45 
less warted and brownish, the contents of which become dif- 
ferentiated into vivacious zoospores, capable, when expelled, of 
moving in water by the aid of vibratile cilia. A similar struc- 
ture has already been indicated in Cystopus, otherwise it is rare 
in fungi, if the Saprolegniei be excluded. In Botrytis and in 
Polyactis, the flocci and spores are similar, but the branches of 
the threads are shorter and more compact, and the septa are 
more common and numerous; the oogonia also are absent. De 
Bary has selected Polyactis cinerea, as it occurs on dead vine 
leaves, to illustrate his views of the dual- 
ism which he believes himself to have 
discovered in this species. “It spreads 
its mycelium in the tissue which is becom- 
ing brown,” he writes, “and this shows 
at first essentially the same construc- 
tion and growth as that of the mycelium 
filaments of Aspergillus.” On the my- 
celium soon appear, besides those which 
are spread over the tissue of the leaves, 
strong, thick, mostly fasciculate branches, 
which stand close to one another, break- 
ing forth from the leaf and rising up per- 
pendicularly, the conidia-bearers. They 
grow about 1 mm. long, divide them- 
selves, by successively rising partitions, 
into some prominent cylindrical linked 
cells, and then their growth is ended, 
and the upper cell produces near its 
point three to six branches almost stand- 
ing rectangularly. Of these the under 
ones are the longest, and they again shoot forth from under 
their ends one or more still shorter little branches. The 
nearer they are to the top, the shorter are the branches, and 
less divided; the upper ones are quite branchless, and their 
length scarcely exceeds the breadth of the principal stem. Thus 
a system of branches appears, upon which, ona small scale, a 
bunch of grapes is represented. All the twigs soon end their 
Fia. 28.—Polyactis cinerea. 
a. Apex of hypha. 
