Rchitioii of Fungi to other Organisms. A. Lorrain SmitJi. 2^ 



such as llie slomalal, bundle and strengthening-, are modified 

 or undevelo|)ed : very rarely does hy|:)ertrophy coincide 

 witli any forward developments. 



A case of parasitism so harmless to the host as to have 

 suggested symbiosis is described by G. R. Sutherland.* He 

 found on the marine alga, Pclvelia canaliculata, the fruits of 

 MycosphacreUa Pehctiae n. sp., and he traced the mycelium 

 o( the fungus permeating the algal tissues in all directions 

 without visibly injuring the host. The fungus in this case 

 evidently lives on the mucilage and other excretions of the 

 loose algal tissues. It fruits on the outer rind of the algal 

 receptacles where nutritive substances would be especially 

 abundant and as the spores issue from the Mycosphaerella 

 perithecia some of them germinate in contact with the 

 escaping oospores of the alga and thus readily infect the new 

 host plant in its earliest stages. 



In true cases of symbiosis there is mutual ach-antage 

 afforded by the two plants one to the other. TluM-e is a 

 delicate balance of gain which ma\' ti|) to one side or the 

 other causing disaster to one of the two plants, symbiosis 

 giving place to parasitism; such varying results are to be 

 found in the root fungus termed mycorrhiaa. 



Mycorrhiza. This name was first used by Frankf to desig- 

 nate the fungi that in their association with the roots of the 

 higher plants vary between parasitism and symbiosis. He 

 distinguished two types — ectotrophic and endotrophic — 

 according as the hyph^e were external or internal. His 

 researches convinced him that the higher plant had become 

 more or less dependent on the fungal hyphte as an intermedi- 

 ary agent between it and the humus of the soil : recent 

 workers have questioned the universal truth of that state- 

 ment. 



Ectotrophic or external mycorrhiza is specially distinctive 

 of the Cupuliferae and Coniferae and also appears in many 

 other trees, shrubs etc. The fungus becomes attached to 

 the outer wall of the root near the tip and then branches 

 and spreads, forming a complete hyphal mantle and destroy- 

 ing the root hairs. Some branches of hypha^ from the 

 mantle spread over the soil or humus on which they feed, 

 others penetrate between the epidermal cells ; they destroy 

 the middle lamellae and split apart the cells of the outer 

 cortex. The growth in length of the root is inhibited and 

 excessive branching is induced, leading to the coral like 

 formation of rootlets characteristic of this type of mycorrhiza. 



Though the hyphcC of ectotrophic mycorrhiza do not enter 



* Sutherland, '15. t Frank, '92. 



