MOULDS. 151 



dendroidal threads of this fungus proceed from a 

 creeping mycelium or spawn of entangled fila- 

 ments which interpenetrates the matrix, upon 

 which it establishes itself. UiDon these threads 

 spherical bodies were long since observed by Dr. 

 Payen, and, under the name of Artotrogiis, described 

 by Dr. Montague as a new species of fungus. Dr. 

 de Bary failed to detect oospores on the mycelium 

 of this mould, although the organs found by Payen 

 in some sort resemble them. De Bary sought in 

 vain, also, for the spherical bodies described by 

 the author above named. It has been calculated 

 that one square line of the under surface of the 

 leaves is capable of producing 3,270 acrospores, 

 each of which yields at least six zoospores, some- 

 times double that number; thus we have 19,620 

 reproductive bodies from that small space. The 

 mycelium from the zoospores is capable of pene- 

 trating the cellular tissue in twelve hours, and, 

 when established there, it bursts through the 

 stomata of the leaves, and fruit is perfected in 

 from fifteen to eighteen hours. Since the zoospores 

 are perfected and ready to germinate in twenty- 

 four hours from their being placed in water, it 

 becomes almost impossible to calculate the myriads 

 of fungi that may be produced from a single centre. 

 Dr. de Bary has also demonstrated that the brown 

 spots so characteristic of the disease are the result 

 of the action of the spores or zoospores. By 

 placing a quantity of spores in a drop of water 



