640 



FUNGI 



germinate 



species which are parasitic on living plants, such as Phytophihora 

 infestans, which produces the potato-disease, and Cystopus candidus, 

 very common on cress and other cruciferous plants, the rapid spread 

 of the disease is caused by the great facility with which the spores 

 are disseminated by the wind ; falling on leaves in moist weather, 



the germinating tube passes through a 

 stomate, and the mycele is developed with 

 great rapidity within the tissue of the 

 host. The most favourable condition in 

 the case of the potato-disease is said by 

 Professor De Bary to consist in an 

 undue thinness of the cuticle, accompanied 

 by excessive humidity, whereby the spores 

 of the fungus will germinate on the sur- 

 face of the plant, sending out processes 

 which penetrate to its interior, though 

 otherwise germinating only on cut sur- 

 faces. 



The Saprolegniese are saprophytic or 

 parasitic fungi, nearly allied to the Pero- 

 nosporr-cK, and differing from them chiefly 

 in two points : although organs are 

 known in many species closely resem- 

 bling the antlicrids of the Peronosporece, 

 the act of impregnation has not actually 

 been observed, the ocispore being, at least 

 in many cases, apparently produced par- 

 ihenogeneticallt/, i.e. without impregna- 

 tion. In some species a single oijspore is 

 produced within each oiigone ; but more 

 often the contents of the latter break up 

 into a number of ob'spores, each of which 

 gives rise to a mycele, or breaks up into 

 zoospores. In some genera, e.g. Achlya 

 (tig. 478), zoospores are also produced in 

 very large numbers by the breaking-up 

 of the contents of zoosporanges, special 

 enlarged cells of the mycele. The well- 

 known salmon disease is caused by the 

 attacks of the parasitic Saprolegnia f&rax 

 on the living flesh of the animal. 



The Mucorini are filamentous fungi, 

 resembling the two last orders in their 

 vegetative development, but differing in 



t heir mode of reproduction. To this family belong some of the most 

 ((million moulds which make their appearance on damp or decaying 

 organic substances. The ordinary mode of i ion -sexual reproduction 

 is by endogenous spores, produced within a sporange (tig. 479, A). 

 The sporanges are borne a1 the ends of sporangiophores, long, erect, 

 imseplated liypha-, springing directly from the mycele or from 

 tlic original germinating filament. Several other kinds of 11011- 



FIG. 478. Two zoosporanges of 

 Achlya. From Goebel's ' Out- 

 Hues of Classification and 

 Special Morphology.' A, still 

 closed ; B, open to discharge 

 the zoospores; a, zoospores 

 ejected, but still resting ; c, 

 zoospores which have left 

 their membrane at b behind 

 them. Magn. about 800. 



