July 31, 1908] 



SCIENCE 



157 



ing a more modern tendency, that sum, again 

 recognized as force, is regarded as due to 

 reactions of (m) upon bodies that transmit 

 force to it. It is clear that neither view pre- 

 serves the scheme of equation (1) ; the first 

 uses the real equilibrium condition of equa- 

 tion (7) in order to exhibit the actual depart- 

 ure from that condition in equation (1), and 

 the second includes forces acting, not upon 

 (m) but upon surrounding bodies. Either 

 view is of course tenable, both within the orig- 

 inal scope of the principle and in the field of 

 modern dynamics to which it has been ex- 

 tended. But it is only in this peculiar sense 

 that d'Alembert made the criterion of equi- 

 librium a basis for the measurement of un- 

 balanced force. 



Frederick Slate 

 Univebsitt of Califoenia 



some apple leaf-spot fungi ' 



Since 1892 leaf-spot disease has been fre- 

 quently reported as doing considerable dam- 

 age in apple orchards in various parts of the 

 TJnited States. Its occurrence has been noted 

 m fifteen different states. Very little seems 

 to be known about the etiology of the disease. 

 That it is a fimgous trouble is indicated by 

 the ease with which it is controlled in most 

 localities by spraying. Gonioihyrium pirina' 

 (Sacc.) Sheldon, Phyllosticta limitata' Phyl- 

 losticia prunicola* Sphaeropsis Malorum' and 

 Hendersonia Mali' have been variously re- 

 ported as causing, or being associated with, 

 the disease. 



The number of fungi found fruiting on the 



'Read before Section G of the American Asso- 

 ciation for the Advancement of Science, January 

 2, 1908. 



•Alwood, W. B., Va. Agr. Exp. Sta., Bull. 

 17:62 (1892). 



"Stewart, F. C, N. Y. Agr. Exp. Sta., Ann. 

 Rep. 14:545 (1895). 



*Tubeuf, Karl Freiher von, and Smith, W. C, 

 Diseases of Plants induced by Cryptogamic Para- 

 sites, 463 (1897). 



• Clinton, G. P., Conn. Agr. Exp. Sta., Ann. Rep. 

 27:300 (1903). 



•Alwood, W. B., Proc. Am. Acad. Adv. Sci., 

 47:41<> (1898). 



leaf-spots is the most confusing thing in de- 

 termining the real cause of the disease. In 

 an examination of apple leaf-spot specimens 

 belonging to the West Virginia Agricultural 

 Experiment Station, the following fungi were 

 found: Coryneum foliicolum, Comothyrium 

 pirina, an undetermined species of the Tuber- 

 culariae (found by Sheldon in the spring of 

 1907), Sphaeropsis Malorum, Monochaetia 

 Mali, Pestalozzia hreviseta, Phyllosticta limi- 

 tata, Torula? sp., Macrosporium sp., Asco- 

 chyta sp., Phyllosticta? pirisedaf, Phoma Mali, 

 Septoria piricolaf, Metasphaeria sp., and an 

 undetermined species of the Leptostromaceae. 

 Of these fungi, only the first four were com- 

 mon enough to indicate any economic impor- 

 tance. Coryneum foliicolum is probably the 

 fungus which has been reported by different 

 writers as a Hendersonia on apple leaves. 

 Coniothyrium pirina wiU be better recognized 

 as Phyllosticta pirina Sacc, from which it 

 was recently transferred by Sheldon.' Conio- 

 thyrium tirolense Bubak, a portion of the 

 original collection of which was examined by 

 the writer, seems identical with C. pirina. 

 Phyllosticta Mali Prill. & Dela. var. comensis 

 Tray, was found to resemble P. limitata in 

 aU characters except the shape of the spot, 

 which in the former is decidedly angular. A 

 part of the type specimen of P. tirolensis 

 Bubak on pear leaves differed from P. limitata 

 by the slightly shorter spores and more gre- 

 garious pycnidia. 



It seems to have been generally taken for 

 granted that Coniothyrium pirina and Phyl- 

 losticta limitata are the most imjjortant fungi 

 causing apple leaf-spot, exceptions noticed 

 being the reports of Clinton' and Sheldon.' 

 Coniothyrium pirina has, on the other hand, 

 been declared by Stewart and Eustace' to be 

 a saprophyte. A more detailed study of the 

 fungus therefore became desirable. 



Pure cultures of it were obtained and grown 

 on the ordinary culture media, with varying 

 success; they were also grown very success- 



' Sheldon, J. L., Torreya 7:143 (July, 1907). 



■ Sheldon, J. L., W. Va. State Bd. of Agr., Ann. 

 Rep. 1:57 (1906). 



■ Stewart, F. C, and Eustace, H. J., N. Y. Agr. 

 Exp. Sta., Bull. 220:228-230 (1902). 



