130 INTERNATIONAL CONGRESS OP VITICULTURE 



Within the haustorium is a small bit of protoplasm in which is imbedded 

 a nucleus. In certain cases the writer has observed two nuclei (PI. II, figs. 

 3 to 5). Istvanffi (1913) has reported as many as four. In his estimation 

 these are produced by the division of a single nucleus which entered the 

 haustorium during the early stages of its development. 



The size of the haustoria is exceedingly variable. According to Istvanffi 

 they are 4 to 10/u, (rarely 15 to 20^0 at their largest diameter by 4 to 12/j. 

 (rarely 20 to 25/i) long. These measurements correspond very closely with 

 those made by the writer. The stems may attain nearly one-half of the total 

 length of the haustorium, varying from 1.5 to 5.5// in length and from .4 to 

 1.0/i in diameter. 



The method of differentiating the cell wall from the haustorium was by 

 the combination of certain stains. After some experimentation, it was found 

 that ruthenium red and methyl green gave the clearest coloration. In this 

 way the cell walls were tinted a deep red and the mycelium green. The 

 safranin-gentian violet orange stain also gives very good differentiation 

 showing the relation to the plasma membrane but since it leaves the cell- 

 wall practically unstained it is unsuitable for that aspect of the problem. 

 A study of sections stained by both methods gives an excellent idea of the 

 relation of parts. 



The formation of conidiophores commences after a sufficient period of 

 mycelial development, the time varying with the organ attacked, the tempera- 

 ture and the humidity. The mycelium begins to mass beneath the stomata 

 forming what has been termed the cushion (PI. II, fig. 6). From these hypae 

 arise many other smaller ones which push upward through the stomata. In 

 order to traverse the small opening they must become greatly attenuated 

 but immediately after their egress they abruptly swell to the normal size 

 of the conidiophore. As many as twenty such branches may arise through 

 a single stomate but more commonly there are from four to six. 



In certain cases the fruiting mycelium may burst directly through the 

 epidermis. This has been observed frequently on flower peduncles which 

 were heavily infected (PI. II, fig. 7). In such cases it appears that the epi- 

 dermal cells are killed, then crushed by the pressure of the mycelium beneath 

 and finally disrupted. There is no evidence that it is a process of solution. 

 On the young fruit the mycelium takes advantage of the lenticle-like struc- 

 tures for its egress. 



The conidiophores are produced most readily in the absence of light, 

 in relatively humid conditions and at a temperature of 18 to 20 C. The 

 other conditions being favorable the temperature is of rather minor import- 

 ance. The method ordinarily employed to obtain an abundance of conidia 

 for germination studies is to enclose infected leaves, on which there is no 

 evidence of conidiophore formation, in a moist chamber during the night 

 (about 12 to 20 hours). A smaller percentage of conidia frequently have 

 been obtained during the day by a similar treatment. The light was in such 

 cases very subdued. This is in accordance with the statements of Istvanffi 

 (1913), Cuboni (1889) and others to the effect that conidiophores are pro- 

 duced only during the night or in subdued light. 



The conidiophores are from 300 to 500^ in height and 7 to 9/A in diameter. 

 Istvanffi states that they average 800 to 1200/x in height and that occasionally 

 one may attain the height of 1500/A. There are usually about six monopodial 



