Jxclalion of Fnuf^i lo other ()r<^a)iis}}is. A, Lorrain Smilh. 19 



common saprophytic brown mould : it g'rew on the sugary 

 exudations from the glands of Clcrodendron fallax leaves, 

 then gradually passed beyond the range of the gland, form- 

 ing conspicuous dead patches on the leaf. Three weeks from 

 the time when the injury was first noted, the spores of the 

 fungus — a series of generations having intervened — were 

 capable of infecting any part of the leaf. 



The closeness of relationship between saprophytes and 

 parasites is also well exemplified in the ftingi that live on 

 insects. iNIiraude* has demonstrated the presence of glucose 

 in the chitinotis covering of insects, located more especially 

 at the place of insertion of the muscles but also spread over 

 the whole surface. It is this substance presumably that 

 attracts and affords sustenance to Lahoulheniae, Saprolegniae, 

 etc. The fungi of these families are true saprophytes, but 

 a case of parasitism has been provedf against a species of the 

 former. Trenomyccs histophthoriis in which a tube from the 

 basal spherical cell of the fungus emerges, pierces the 

 cuticle of the insect and feeds on the adipose tissue, without, 

 however, doing much injury to the host. 



Method of parasitic attack. The fungus spore on germina- 

 tion emits a tube which is a very delicate structure. The higher 

 plants are easily protected from its attack as to the trunks 

 and branches by layers of cork — subject however to wounds 

 and cracks ; and as to the leaves by a covering cuticle which 

 is interrupted at intervals by stomata. The germinating 

 fungus most frequently gains entrance through these 

 accidental or natural openings, and after reaching the 

 interior the mycelium develops haustoria which pierce the 

 living cells. 



Certain leaf-fungi directly enter the host by piercing the 

 cuticle. In the case of Botrytis cinerea a facultative parasite 

 of the lily, Blackman and Welsfordt have shewn that after 

 germination the spore tube from the side lying against the 

 leaf produces a peg-like outgrowth which pierces the cuticle 

 by mechanical pressure alone. The large family of 

 Erysiphaceae and such epiphyllous genera as Asterina and 

 Mcliola^ form haustoria at intervals along the creeping 

 hvph^e which pierce the cells of the leaf and extract the 

 required nourishment. It is only the larger hyph,?e that 

 form these haustoria, thcnigh the finer filaments may attack 

 the cuticle to some extent. 



The position of the hvpha^ within the tissue varies with 



* Miraude, '15. + Chatt. & Pic, '08. 



X Black. & Wels., 'i6. § Maire, '08. 



