636 FUNGI 



and to creep over neighbouring surfaces, thus far resembling in all 

 respects a colossal ramified Amoeba. The plasmodes are often found 

 to have taken up into them and enclosed a great variety of foreign 

 bodies, such as the spores of fungi, parts of plants, &c. They are 

 curiously sensitive to light, and may sometimes be found to have 

 retreated during the day to the dark side of the leaves, or into the 

 recesses of the tan over which they had been growing, and again to 

 creep out on the approach of night. Under certain conditions the 

 swarm-spores may lose their power of motion and become encysted ; 

 they are then known as microcysts, and may remain in this resting 

 condition for a considerable time, especially if desiccated. If again 

 placed in water, they return to their motile swarming state. The 

 plasmodes may also enter a resting state, in which they assume a wax- 

 like consistence, and dry up into a brittle horny mass. They are then 

 known as sclerotes. In a few genera the spores are not contained in 

 sporanges, but are borne on external supports or sporophores. But 

 in the great majority of genera the plasmode becomes ultimately 

 transformed into sporanges (B, a, a! , b) ; either each plasmode 

 becomes a single sporange, or it divides into a larger or smaller 

 number of pieces, each of which undergoes this transformation. 

 When mature, the cavity of the sporange is either entirely filled 

 with the very numerous spores, or in most genera tubes or threads of 

 different forms occur among the spores, and constitute the capillitium. 

 These capillitium-tubes have often a spiral appearance, owing to 

 irregular thickenings of the cell- wall, and are very beautiful objects 

 under the microscope. The growth of many species of Myxomycetes 

 is exceedingly rapid, going through their whole cycle of development, 

 with its various phases, in the course of a few days. 



The ChytridiaceSB are a group of minute microscopic fungi showing 

 an affinity in some respects to the Myxomycetes, and even to the 

 infusorial animalcules. Their ordinary mode of propagation is by 

 zoospores bearing one or two cilia, which either germinate directly 

 or conjugate to produce a resting-spore. They are parasitic on fresh- 

 water organisms, both animal and vegetable ; and their chief interest 

 to the microscopist is that their zoospores have apparently frequently 

 been mistaken for antherozoids of the ' host.' 



The Ustilagineae are fungi parasitic on flower ing plants, attacking 

 the stem, leaves, and other parts, where they form brown or yellow 

 spots. They are often exceedingly destructive to vegetation, causing 

 the diseases of cereal crops known as bunt, smut, &c. The course 

 of development of these fungi is not yet in all cases accurately 

 known. The mycele, consisting of slender segmented hyphse, spreads 

 extensively within the tissues of the host, and bears spores which 

 either reproduce the mycele again directly, or with the intervention 

 of so-called ' sporids.' 



The TIredineae afford the most remarkable illustration among 

 fungi of the phenomenon already mentioned, that of alternation of 

 generations ; forms previously considered to belong to widely separated 

 groups being now known to be stages in the cycle of development of 

 the same species. A striking instance of this is furnished by the 

 well-known and very destructive disease of wheat and other grasses 



