BACTERIA. FUNGI. 



165 



proportion as the one end elongates the other dies away. Hence tlie same effect is 

 produced as if the progressive motion of these hyphfe were like that of ship-worms. 

 This impression is particularly sti'ong in cases wherein one part of the mass of 

 wood attacked exhibits hyphre occupied with their mining operations and growing 

 through jjartition walls, whilst the otlier part has been the scene of past activity, 

 and exhibits numbers of drilled holes, but no longer any trace of hyphas. The fact 

 that a plant is thus invaded internally by the parasitic mycelia of fungi is not 

 always betrayed by its external appearance. Sometimes the hosts remain somewhat 

 backward in development, but this circumstance might be just as well due to other 

 causes, perhaps to unsuitability of situation. It is not till the mycelia need once 



"Zu 



Fig. 32.— Hyphic of Parasitic Fungi. 

 1 Of one of the Peronosporeae. 2 of a Mildew, s of one of tlie PolyporeEe. 



more to multiply and distribute their kind that they emerge partially fi'om the 

 host; they then lift their spore-forming hyphas above the surface, leaving it to the 

 wind to distribute the spores as they are detached. 



This process vividly recalls the similar behaviour of those water-plants which, 

 in a similar manner, vegetate submerged for months, and only come to the surface 

 at the tlowering and fruiting seasons, in order to expose their flowers to insects, 

 and their seeds to the breeze. We are also reminded of the saprophytic orchids 

 already described, which nourish themselves and grow for years imbedded in the 

 humus of woods, and then seize the opportunity affoi'ded by a favourable sunnner 

 to raise up in a few weeks flowering stems above the bed of the forest. As a rule 

 the spore-bearing hyphse, emerging from the hosts of parasitic fungi, are highly 

 conspicuous both in form and colour. As well-known instances we may here 

 mention the powdery, rust-coloured, chocolate-broM^n, or coal-black masses of spores, 

 known by the names of rust and smut; the mealy, orange-coloured masses which 

 make their appearance on the green stems and fruits of roses (.iEcidium stage of 

 Phragmidiuvi subcorticum), and the discomycetous Peziza Willkommii, which 

 is parasitic in the branches of green larches, and exposes its fructifications beyond 



