XATURAL HISTORY SOCIETY OF GLASGOW. 295 



of the leaf peridia fringed with recurved teeth. These peridia are 

 either scattered over the surface or collected in tufts and clusters. 

 Sometimes they are elongated (as in Roestelia and Peridermium), 

 and open by lateral fissures or a lacerated mouth or burst irregularly. 

 Inside the cups moniliform chains of spores are produced. Growing 

 from the same mycelium, usually appearing before the peridia and 

 on the upper side of the leaf — though sometimes on the same 

 surface as the peridia — are flask-like bodies known as spermogonia, 

 which are clothed with very fine threads that protrude like a brush 

 from the mouth, and which contain besides a very minute dust, 

 spermatid. These spermogonia have long been surmised to be 

 connected with the sexual reproduction of the fungus, but as yet 

 all their bearings on the life-history of the plant have eluded obser- 

 vation. The largest spermatia that have been examined are only 

 g-gVo i ncn l° n 8' D y roo!ooo ^ ncn across > but the length of many is 

 not more than this width. 



On cereals and other grasses, and generally on many plants in 

 early summer, examples of Uredo or rust are frequent. From the 

 mycelium tufts of branches are given out towards the surface, and 

 each of these bears a roughish spore at its tip — not a chain of spores 

 as with iEcidium — and, from the mass of such spores, rusts are 

 usually very conspicuous. These spores are most frequently brown, 

 but sometimes yellow. 



Later in the season teleutospores appear. If these are single- 

 celled, the parasite is known as Uromyces; if two-celled, as Puccinia 

 or Gymnosporangium ; if there are three cells side by side, as 

 Triphragmium ; if three or more cells in a row, as Phragmidium. 

 These spores usually germinate after a period of rest. The mildew 

 on wheat (Puccinia graminis) is one of the best known examples 

 of this stage. Its spores grow from the same mycelium as the rust 

 ones (Uredo linearis), but, while these rust spores are orange, 

 roundish, and somewhat rough, the others are elongated, club-shaped, 

 and — though brownish under the microscope — black in mass to the 

 naked eye. 



So long ago as the end of last century the barberry bush had 

 been almost extirpated in some parts of England, as farmers had 

 become convinced that it was a fruitful source of mildew in wheat. 

 Botanists were, however, inclined to regard this as a vulgar error. 

 About seventeen years ago Prof, de Bary of Strasbourg, by 

 experiment and observation, satisfied most continental botanists 



VOL. V. X 



