DIV. I 



THALLOPHYTA 



441 



an antheridium. These are uninucleate cells, separated from the mycelium by 



The male nucleus passes into the 



partition walls, and stand close together, 

 oogoninm by an opening which forms in 

 the cell walls (Fig. 382, 1-4). After fertilisa- 

 tion the oogonium is surrounded by invest- 

 ing filaments which spring from its stalk 

 cell or from that of the antheridium (5), 

 and the oogonium itself becomes converted 

 into a multicellular structure (6). In Sphae- 

 rotheca the ascus containing eight spores 

 arises from the binucleate penultimate 

 cell, while in Erysibe and Phyllactinia this 

 cell exclusively or mainly produces asco- 

 genous hyphae which in turn give rise to 

 the numerous asci. Before entering upon 

 the formation of perithecia, the Mildew 

 Fungi multiply by means of conidia ab- 

 stricted in chains from special, erect hyphae, 

 from the tip downwards. These are distri- 

 buted by the wind. The Mildew Fungus 

 occurs on the leaves and berries of Vitis 

 in America and has appeared in Europe 

 on the Grape-vine since 1845. This fungus, 

 known as Oidium Tuckeri, is the conidial 

 form of Uncinula necator (-U. spiralis), 

 the small perithecia of which have append- 

 ages spirally rolled at their free ends and 

 are only rarely found (Fig. 383). 



Order 2. Plectascineae 



The spherical perithecia have a closed 

 peridium ; the asci are irregularly arranged 

 within this. * 



1. Aspergillaceae ( 66 ). Fructification 

 small ; not subterranean. Here belong 

 two of the most common Mould Fungi, 

 Aspergillus (Eurotium) herbariorum and 

 Penidllium crustaceum, which live saprophytically on organic substances. Both 

 multiply extensively by means of conidia before they begin to form perithecia. 



In the case of Aspergillus herbariorum, the conidia are abstricted in chains 

 from a number of sterigmata arranged radially on the spherical, swollen ends of 

 the conidiophores (Fig. 384). The conidiophores are closely crowded together, 

 and constitute a white mould, afterwards turning to a blue-green, frequently 

 found on damp vegetables, fruit, bread, etc. Some species of Aspergillus are 

 pathogenic in man and other mammals ; thus A. fumigatus, which lives in 

 fermenting heaps of hay at an optimum temperature of 40 C. ( 6 ~), causes mycosis 

 of the external ear, the throat, and the lungs. 



In Penidllium crustaceum, another widespread blue-green mould, the erect 

 conidiophores (Fig. 384) are verticillately branched. The spherical perithecia of 

 Aspergillus and Penidllium are produced later on the mycelium, but only rarely 

 occur in the latter genus. They develop from the sexual organs consisting of 



FIG. 383. Uncinula necator. A, Conidial 

 stage ; c, couidium ; 5, conidiophore. B, 

 Hypha which has formed a disc of attach- 

 ment (a) and has sent a haustorium (ft) into 

 an epidermal cell. C, Perithecium with 

 appendages. (From SORAUEB, LINDAU, 

 and REH. Handb. d. Pflanzenkrankheiten, 

 ii. p. 194. 1906.) 



