132 " Black Neck " or Wilt Disease of Asters 



but germinate within the sporangium (Fig. 16). In some cases the 

 discharged zoospores at first remain aggregated together and show 

 very sluggish amoeboid movements, altering their shape as they move. 

 Gradually, however, they separate from one another and begin to swim 

 about vigorously as most of the zoospores do from the first. In motion 

 the zoospores continually alter their shape but generally are somewhat 

 kidney-shaped with a median furrow (Fig. 18). They possess two 

 vacuoles which appear to lie one on either side of the furrow, and two 

 unequal cilia springing laterally from the middle of the depression. 

 When moving the zoospore progresses in the direction of its longer 

 axis, one cilium lashing forwards and the other trailing behind. After 

 swimming for about half an hour they come to rest (Fig. 19) and imme- 

 diately begin to germinate by means of a germ tube which soon branches 

 (Fig. 20). In water alone these germ tubes do not grow much further, 

 but on nutrient media they give rise to a normal mycelium. In hanging 

 drops containing a piece of the root of an aster seedling, the germ 

 tubes almost immediately penetrate the tissues and produce a mycelium 

 within. 



After the liberation of the zoospores the hypha forming the stalk 

 of the sporangium grows into the empty sporangium and then forms a 

 new sporangium within the first (Fig. 21). As many as three sporangia 

 are in some instances thus formed within one another (Fig. 22). 

 Variations also occur in which the proliferating hypha grows out of 

 the empty sporangium before forming the new sporangium (Fig. 22). 

 So far as I am aware this proliferation of sporangia has not been 

 previously described for any species of Phytophihora, although De Bary 1 

 describes and figures similar examples in Pythium proliferum and 

 P. megalacanthum. 



Fusarium. 



The vegetative characters of the species of Fusarium so frequently 

 present on the decaying portions of the stems of diseased asters render 

 this fungus easily distinguishable from the primary cause of the disease. 

 The mycelium branches much more freely than that of the Phytophihora 

 (Figs. 23 and 24), it stains yellow with iodine and also with Schultze's 

 solution and its walls give none of the reactions characteristic of cellulose 

 The hyphae are abundantly septated, with individual cells containing 

 several nuclei and characteristic oil globules, but none of the regularly 



1 Bot. Zeitung, 1881, pp. 559-623, 



