Lecture on the Parasitic Fungi of the British Farm. 395 



Fig/ 17. Threads from a Polyporus. 



{vide Fig. 16) is here given, very highly magnified. The 

 effects of all these pass by one designation, dry -rot. I will now 

 describe its progress. The first signs are small white points 

 from which a filamentous substance 

 radiates parallel with the surface of 

 the wood. This is spawn, which, as 

 it gains strength, insinuates itself into 

 any crevices however minute, and the 

 threads are so fine that they pass be- 

 tween the tubes from which the wood 

 is organized, and forcing;^ them apart, 

 destroy all cohesion. (See Fig. 17.) 

 This diagram shows these threads 

 from one of the polypori. Sometimes 

 various spawns interlace and form a 

 tough stratum; and the rapidity and 

 force of increase are such as to cause, 

 under favourable circumstances^ the 

 total ruin of the wood. From the 

 experiments previously described on 

 the growth oifungals, you will perceive 

 that the acidulation of the fermenting 

 sap promotes their growth. Kyanizing, or the application of 

 coj^rosive sublimate, has been resorted to as a preventive. An 

 experiment may be made to show its effects : a solution of fish- 

 glue will be found to yield fungi in abundance, but if corrosive 

 sublimate be mixed with it none appear, and the same result will 

 follow additions of certain preparations of copper and other 

 mineral poisons. Oak felled in the spring, when full of sap, is 

 almost sure to have dry-rot, therefore that which is destined for 

 farm erections should be cut in winter, for otherwise the only 

 chance of stopping the appearance of the fungi is to substitute 

 some poison by saturation for its proper juices, or to force them 

 out by an objectionable pressure. Immersion in water is bene- 

 ficial, but heat applied to dry the wood only hastens the malady. 

 In Brest dry-rot is said to be unknown, and all the timber used 

 in its yards is kept in a creek of the harbour. 



VI. Fungi of a different kind from any yet described follow 

 the British farmer into his dairy, and interfere with his household 

 economy. Penicillium and aspergill are two terms applied to 

 some of them, because in their microscopic appearance, given in 

 the delineation before you, they resemble sprinkling brushes. 

 (See Figs. 18, 19.) Fig. 18 represents the Penicillium \evy highly 

 magnified. Aspergill is shown in Fig. 19. They are sufficiently 

 indicative of their names. Penicillium is the mould on hay, as 



