64 British UredinecE and UstilaHnecs. 



spores." The spore-formation itself is similar to that of 

 Ustilago,* and, commencing above, proceeds downwards. 



Sorosporiuui. — The spore-formation in Sorosporium 

 differs considerably from that which has just been described 

 in Ustilago, although it is obviously of the same type. In 

 Ustilago the mature spores are separate and distinct, form- 

 ing usually a pulverulent mass. In Sorosporium, on the 

 other hand, they are in their perfect state aggregated into 

 spore-balls, which individually often contain fifty or a 

 hundred separate spores. The process of spore-formation 

 has been studied by Von Waldheim with 5. saponaricB, 

 and is as follows : — The mycelium, which is very abundant 

 in the blossom and ovary, rapidly changes into spore-form- 

 ing hyphae, from 4 to /^u in diameter, which are gelatinous 

 and full of shining protoplasm. The free ends of these 

 hyphae have a tendency to curve inwards and roll them- 

 selves up (Plate V. Fig. 9). The spore-forming hyphae 

 from several contiguous mycelial branches, incline together, 

 and twist themselves into a ball, as happens in the forma- 

 tion of a lichen thallus. These convoluted and contorted 

 spore-forming hyphae, being gelatinous, soon become so 

 intertwined and entangled that they cease to be indi- 

 vidually recognizable ; to all appearances they coalesce 

 together in part, if not entirely, and on the exterior of this 

 gelatinous ball other hyphae are now seen encircling it 

 (Plate V. Figs. 10, 11). These latter, also being gelatinous, 

 soon lose their individuality, although at times traces of 

 their concentric arrangement can be made out. Spore- 

 formation takes place only in the central gelatinous ball, 

 in the middle of which it commences by the central part 

 darkening in colour and becoming differentiated into 

 spore-like bodies, which vary in number from four to 

 sixteen. Apparently these bodies again - subdivide, so 



* De Bary, " Vergleichung, " p. 187. 



