STRUCTURE. 



45 



less warted and brownish, the contents of which bocome 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, on a small scale, a 

 bunch of grapes is represented. All the twigs soon end their 



j 



FIG. 28. Polyactis cinerea. 

 a. Apex of hypha. 



