66 TRANSACTIONS AND PROCEEDINGS OF THE [Sess.lv. 



woody mass like a tuber. It is true, the cause of them is 

 not vegetable but animal. One of the gall-midges deposits 

 along with its egg a certain plasm, and this diverts the juices 

 and tissues of the bud into an abnormal mass called a gall. 

 In the same way the granules of P. infcstans, invading the 

 underground buds of the potato-stems, divert the starch of 

 the plants into tubers. And as these tubers are infested in all 

 parts, but particularly around the eyes, with the mucoplasm- 

 granules, the germinal elements of the parasite are carried 

 from one race of potatoes to the following, and from one season 

 and country to another, not requiring invasion from without 

 for new displays of the disease. Many trees are similarly 

 haunted by their peculiar parasites, the plasm of which is 

 carried by subdivision in the growing tissue from one season's 

 leaves to another. And hence the impossibility of curing the 

 disease of the coffee plant. Eecords exist of narrow escape 

 from extirpation of some of our forest-trees by leaf-parasites. 

 When once the young seedling has its roots invaded by the 

 mucoplasm of its proper parasite, the parasite and the host 

 go on leading a symbiotic life as long as the host lives, the 

 parasite sometimes breaking out and fruiting itself, and 

 sometimes lying quiescent in its mucoplasm granules. This 

 theory fully explains all the phenomena of such parasitism ; 

 while the theory that assumes spores to be carried by the 

 wind from one plant to another is destitute of a philosophy, 

 and wholly shirks the question of where the first spore comes 

 from. Eor resting-spores or any element of the non-parasitic 

 system of a fungus do not give rise to the conidia of the 

 fruited and matured parasite ; they give rise only to the 

 mycelium and mucoplasm, which is the true initial stage of 

 the parasite, the form in which it can alone be absorbed into 

 the higher plant. And this theory will also help to explain 

 the transmission of the parasites of animal and human 

 diseases from one generation to another. 



