318 XXIII. BEPRODUCTION OF FUNGI. 



If note is not made of these relations, the fructifications of these 

 two parasitic fungi might be regarded as belonging to the Mucor 

 itself. 



Moist Chamber Cultures of Micro-Fungi. In the cultivation 

 of fungus spores in moist chambers it may be remarked that 

 for rapid cultures the pasteboard chambers answer admirably ; 

 but that for cultures which last more than a few days they 

 cannot be used, as they themselves form a nidus for the spores 

 of various moulds. Glass chambers (p. 279) must then be used. 

 The infusion of horse-dung recommended for Mucor does not keep 

 for long, and therefore can be recommended only for cultures 

 of rapidly-developing moulds. If the development requires a 

 longer period, it is sometimes feasible every other day to remove 

 the drop carefully with a pipette, and replace it with a new 

 supply. The infusion keeps the longest when the dung is 

 stirred in water, boiled and filtered, and the filtrate kept for 

 at least twenty-four hours in a vapour bath. In many cases 

 a cold extract of dried fruits, such as raisins, pears or plums, 

 is very serviceable. Such an extract is filtered till clear, and 

 then evaporated to the thickness of syrup. It can be kept for 

 years unchanged, and when wanted for culture purposes can 

 be mixed in suitable proportions with well-boiled water. If the 

 fluid has an acid reaction it must under some circumstances be 

 neutralised with ammonia, as many fungi cannot endure the 

 acids derived from fruits. 



The Potato Disease, Phytophthora infestans. The cause of 

 the potato disease is likewise a Phycomycete, Phytophthora in- 

 festans, de Bary, the germ- tubes of which penetrate through 

 the membranes of the epidermal cells of the potato-leaf into 

 its intercellular spaces, and, spreading about in these, destroy 

 the tissue of the host -plant, forming brown spots of constantly- 

 increasing diameter. In order to obtain the fungus in quantity 

 in a fructifying state, we place a piece of a diseased potato-plant 

 in an atmosphere saturated with moisture under a bell- jar, and 

 let it lie there for about two days. The diseased leaves are 

 now covered over on both sides, but especially on the under, 

 with white " mould," formed by the filamentous fruiting branches 

 (gonidiophores) of the Phytophthora, which are especially de- 

 veloped at the edges of the brown spots. On surface sections 

 of the parts thus covered we see the gonidiophores projecting 

 through the widely-opened stomata. We can demonstrate this, 



