120 



FHYCOMYCKTES. 



tufts, iuul tt)nii a white bonier round the brown parts of 

 the leaf; they are monopodially branched and produce terminal 

 sporangia (gonidia), which are easily detached. The sporangia 



on germination either pro- 

 duce a varying number of 

 zoospores, or germinate 

 directly like conidia to form 

 a mycelium capable of pro- 

 ducing new conidia. The 

 potato -disease is distin- 

 guished from Phyto])htliora 

 omnivora in the absence 

 of sexual reproduction by 

 oospores.^ It is generally 

 assumed that the mycelium 

 hibernates in potato-tubers, 

 from which the fungus 

 recommences to spread in 

 spring. Boehm,- however, 

 contests this, and holds the 

 hibernation of the fungus 

 to be quite unknown, and 

 that from the tubers of 



Fio. 31.-Suiface of a Beech-seedling with swarm- a disCaSCd plant, either a 

 spores a, h ; the germ-tubes from tliese penetrate ^ 



between adjacent epidermal cells ; c, sporangium with health V plant Or llOUC at 

 zoospores already germinating inside it, d, f\ e, -a J r , 



germ-tube which has penetrated directly into an all reSultS 

 epidermal cell; jr, germ-tube which, after growing 



<!Aiter*R"Hanr V ''^"' '''^'' '''^'''" ""^'^^ "^ '^'^^ *""*■ '^'''^ Phjituplitliom potato- 

 disease is quite distinct from 

 {(i) the potato-blight or wet-rot which, according to Boehm, is the 

 result of closing up of the lenticels, with a consequent stoppage 

 of respiration ; {h) bacteriosis, which will be considered amongst 

 the bacterial diseases of plants. 



Lagerheim^ has pointed out that Solanum murimtiim 

 much cultivated in Ecuador on account of its edible fruit, has 

 been for many years subject to attack from Fhi/tophthora 

 in/cstam ; the fruits sicken and rot off before ripening. The 



rhis is a well-known point of controversy, for an intei-esting discussion of 

 ;h we would refer to " Diseases of crops," Worth. G. Smith, 1884. (Edit.) 



• Thi 

 ,hich we woukl refer to " Diseases of crop 

 2 Boehm, SitzwKjsber. d. Zool.-hotan. Ges., Vienna, 1892, 

 •' Rivista Ecuatorinna, 1891. 



