THE INFECTION OF THE HOST. 33 



plant, and may be seen in the piiniarv cortex, in tlie medulla, and in 

 the nu'duUaiT rays of the first shoots of each period of vet^etation, 

 but ha«s not been ol)served in the soft bast. With the l)eginning of 

 the new season of growth the mycelium, according to Sadebeck, 

 extends into the leaves of the young shoots, penetrates first the inner 

 tissue of the leaves, and finally progresses to the development of the 

 subcuticular hymenium. From what foundation of experimentation 

 Sadebeck has arrived at these views respecting this jjarticular species, 

 I am unable to state, but he has given the outlines of his inxestigations 

 upon other species.' 



The facts given by De Barv" can not be cited here, for this work 

 was done upon the Exoascus infesting the cherry tree, and which is 

 now considered to be distinct from E. deformans. 



The general acceptance of the view that spring infection of the peach 

 foliage is largely due to the extension of the internal perennial myce- 

 lium into the new shoots and leaves from the shoots of the previous 

 sunnner, has ])roba)>lv considera])ly I'etarded the progress of prevent- 

 ive treatment. Pathologists have thought it improbable that an}'^ 

 considerable amount of disease could be prevented after a tree was 

 once generally ati'ected, as the perennial mycelium, being internal, 

 could not be readily reached by external sprays. Prillieux,* writing 

 In 1872, advises the gathering of the diseased leaves and the cutting 

 away and burning of the diseased ))ranches. Frank * has made like 

 recommendations in both editions of his work on plant diseases. 

 Assuming the mycelium to be perennial, he says that the curing of the 

 disease might be aimed at through cutting back of the diseased branches 

 and the prevention through quick removal of the diseased leaves. 

 Winter' suggests a somewhat similar line of treatment, with the 

 additional recoumiendation that the trees be protected from rain 

 during the unfolding of the leaves. Dr. Cobb,® as late as 1892, after 

 speaking of the perennial' mycelium of this fungus, discusses pre- 

 ventive and curative measures, such as tbe destruction of diseased 

 leaves, prunings, etc., while in the more severe cases he says the 

 sooner the trees are cut down and burned the better it will be for the 

 peach industry. 



^Sadebeck, Dr. R., Die parasitischen Exoasceen, Hamburg, 1893, pp. 24-28. — Das 

 perennirende Mycel der Exoascus-Arten. 



'■'De Bary, A., Com. Mor. and Biol, of the Fungi, Mycetozoa, and Bacteria, Eng- 

 lish edition, 1887, p. 266. 



=* Prillieux, Ed., Bui. de la soc. bot. de France, 1872, T. XIX, p. 2.30. 



* Frank, Dr. A. B., Die Krankheiten der Pflanzen, Breslau, 1881, Part II, i). 526; 

 second edition, 1896, Vol. II, p. 250. 



^AVinter, Dr. Georg, Die durch Pilze verursachten Krankheiten der Kulturge- 

 wiichse, Leipzig, 1878, p. -17. 



"Cobb, Dr. N. A., The Agricultural Gazette, Sydney, New Soutli Wales, 1892, Vol. 

 Ill, pp. 1001-1004. 



19093— No. 20 a 



