330 



couceutric circles of uniform breadth about the point of infection. Finally 

 the fruit is mummifiecl, and according to Dandeno ('00)^ there seems to 

 be a distinct production of cellulose in the cell-wall of the apple, and also 

 a production of starch in the invaded cells. The walls become thick and 

 the fruit is temporarily' in a state of preservation. 



ETIOLOGY 



Tlie disease is caused by a fungous parasite, SiJliaeropsis maloriDn. 

 Its general nature is that of a wound parasite, though it frequently fol- 

 lows blight, thus acting as a saprophyte. Its pathogenicity has been es- 

 tablished by Paddock ('00)- and by Scott and Rorer (1. c, p. 49). The 

 writer lias confirmed the work of these men, but at present the results 

 are not entirely satisfact(n\v. In few cases luis the canker been produced 

 by artificial inoculation even midcr the most favorable conditions. The 

 only explanations at hand are that the fungus is strictly saprophytic or 

 tliat tlie work was not done at the right season of the year. Where maxi- 

 nnun sterile conditions were maintained and where the inoculations were 

 iiiado in early summer the wi'itcr has failed (o rciiroduce the canker dis- 

 ea.se. Further (>xt»eriments may show, however, tliat infection is possible 

 if done at earlier seasons, i)erhaps at tlie time of the rise of sap. Leaves 

 liave been iimcnlalcd in all ciiiic('i\;il>lc iiianncr. hut only where spores 

 were sprayed on the under side were we able to produce "frog eye." :n 

 these cases abundant fruit bodies appeared. Extended discussion, as re- 

 gards the iialhogcnicily of tlic organism cannot be taken u\) here, but it 

 may be said that the present state of our knowledge is very unsatisfactory 

 and many experiments will l)e necessary to clear up these i)oints. 



Syiiononijj. — In literatui'e we find tlie fungus referred to as Spha-cr- 

 opsi.s malanim lierk. and »S'. iiiulondit I*k. Oilier names have been apiilied 

 to the same species, so tlnit it is only by making a careful outline of the 

 work done, tracing it from its discovery to tlie present time, that tiie sit- 

 uation may become clear. 



Berkeley (':>IJ)'' foiuid ;i lungiis wliicli lie called Sphdcria iinilonnii. 

 He described it ;is follows: "(ilobnse or snhglobose, covered with a black- 

 ened cuticle; stroma lilackish, cuticle erumpent, more or less strcmgly 



''06. Dandeno, J. B. A Stimulus to tho Production of Cellulose and Starch. Kept. Mich. 

 Acad. Sci. 8:40-44. 1906. 



»'00. Paddock, W. The New York Apple Tree Canker (Second Report) N. Y. (Geneva) Art. 

 Exp. Sta. Bui. 185:205-213. 1900. 



>'36. Berkeley, M.J. English Flora 5:257. 1836. 



