1920] A Little Known Vetch Disease 77 



their presence without access to serial sections of material embedded in 

 paraffin. Setae on leaf lesions can best be demonstrated by stripping 

 off the epidermis and making examination with the microscope, Fig. 

 21. Here acervuli will be found which have as few as a single seta or 

 even none, whereas adjacent^ acervuli bear as many as six to eight. 

 Setae have not been observed on affected pods, although many serial 

 microtome sections of j^oung and mature lesions have been studied. 

 Since the setae do not stand perpendicular to the leaf surface, it 

 would be difficult to get an entire seta in vertical section and they may, 

 for this reason, have escaped detection. Furthermore, their presence 

 in the genus Colletotrichum is known to be so variable that it is entirely 

 possible that they are never formed in pod lesions. These seta are 

 from two to three times the length of the conidiophores, are brown in 

 color, either one-celled or at most, one-septate and gradually taper to 

 a blunt point. 



Nuclear phenomena 



Since Protocoronospora was provisionally placed in the Thelepho- 

 raceae, a family in the order Hymenomycetineae whose members pos- 

 sess basidia which are binucleate in the young condition and which 

 arise from binucleate cells in the subhymenium, it was believed that 

 a study of the nuclear conditions in this parasite would be of prime im- 

 portance in determining its systematic position. Certain hymeno- 

 jnycetes have, of course, been described the cells of whose carpophores, 

 except the hymenial portions, and the nutritive mycelium were either 

 uninucleate or multinucleate." 



Accordingly lesions on stems, which were found to be more favor- 

 able for study than those on other parts of the plant, were sectioned 

 and stained with Flemming's triple stain in a manner previously 

 stated. The nuclei were found to vary greatly in size, a condition 

 Avhich has been noted in many other fungi. The largest nuclei measure 

 about 3[x in diameter and are most easily observed in the cells at the 

 periphery of the acervulus, either within the epidermis or within 

 the more deeply lying host tissue. Here the hyphal cells are found to 

 contain one to five nuclei (Figs. 14 and 16). The conidiophores and 

 stromatic cells directly beneath them are found to possess consider- 

 ably smaller, more numerous nuclei, since as many as twelve is not 



" An excellent review of this situation with a bibliography of all of the important con- 

 tributions to the subject is contained in a recent paper bv Pitzpatrick. H. M. Crytology 

 of Eocronartium musicola. Am. Jour. Bot. 5: No. 8, pp. 399-419, Pis. 30-33, 1918- 



