( 6i ) 



CHAPTER IX. 



FORMATION OF THE TELEUTOSPORES OF THE 

 USTILAGINE.E. 



While it is true that the spores of Ustilagineae are formed 

 from the mycelium, yet the process does not take place 

 directly from the vegetative mycelium which has just been 

 described. On the contrary, at those favoured parts of the 

 affected host-plant at which the spores are developed the 

 vegetative mycelium often quite suddenly changes its 

 character. The double-contoured hyphae with pellucid 

 vacuolate contents lose their double contour, become 

 swollen or distended, and contain, instead of a clear watery 

 fluid, a gelatinous, granuUr protoplasm in which numerous 

 oleaginous particles may often be seen (Plate V. Figs. 2)-^)- 

 The gelatinization of these spore-forming hypha; is a great 

 character of the Ustilagines ; it does not, however, occur 

 in all species. The first change observable in the mycelium 

 before it becomes a spore-forming hypha, is that its walls 

 increase in thickness at the expense of its calibre, which 

 becomes proportionately diminished ; soon, however, the 

 whole hypha becomes dilated, so that its lumen is increased. 

 Its contents can now, by the action of reagents, be shown 

 to consist of protoplasm. Spore-formation takes place, 

 after these changes in the mycelium, so differently in the 

 different genera that it will be necessary to describe the 

 process, as it takes place in each one, separately. 



