376 SUMMARY OF CURRENT RESEARCHES RELATING TO 



be identical with Oidium haplophylli P. Magn. recorded from Palestine. 

 From the characters given, Traverso concludes that the species belongs 

 to the genus Ovulariopsis, and represents the conidial_ stage of Erysiphe 

 taurica, which grows on plants of several different families. 



Development of Polystigma rubrum.* — The material on which 

 this research was made by Wilhelm Nienburg was collected and fixed at 

 intervals of fourteen days from the middle of July onwards to the 

 middle of March. Many diseased leaves were kept under observation 

 during the winter. During the autumn the leaves attacked by the 

 fungus were plucked and destroyed before falling, and the disease by 

 this means was stamped out, proving that infection was carried on by 

 means of the ascospores and did not winter in the buds. 



The archicarp begins to develop when the stroma has reached a 

 considerable thickness. At that stage the cells of the plum-leaf are 

 pushed apart by the hyphae ; the upper and lower epidermis are still 

 intact, but the cells of the mesophyll are mostly killed. The archicarp 

 forms a coil of darker coloured hyphae rich in plasma contents. 

 Certain hyphae, sometimes considered as trichogynes, emerge from the 

 stomata to the outer surface, but they are purely vegetative. The 

 " coil " is formed of (1) a cell with several nuclei ; (2) an elongate 

 cell which contains only one large nucleus ; the following cell is shorter 

 but also uninucleate. The two cells next in the coil possess two small 

 nuclei each, the remaining cells having a number of smaller nuclei. A 

 nucleolus is conspicuous only in the large solitary nuclei. The end of 

 the coil disappears in the vegetative tissue ; no trichogyne was at that 

 time formed. In every archicarp there were thus found in order (1) a 

 long cell with many nuclei ; (2) a long cell with a large nucleus ; and 

 (3) a short cell, also with a large nucleus. These stages were observed 

 in material collected in the end of July or the beginning of August. 

 Later in the season there were developed many-celled branches from tbe 

 archicarp, considered by Nienburg as trichogynes. One branch was 

 directed towards the leaf -stroma, but disappeared below the epidermis ; 

 another branch grew towards the upper surface of the leaf. Nienburg 

 came to the conclusion that these branches took no part in fertilization. 



The two important cells were the long multinucleate cell, and the 

 neighbouring equally long cell with the one large nucleus. The former 

 he considers as the antheridium, the latter the ascogonium. He found 

 a thin area in the wall between the two cells even before the ascogonium 

 had reached full development. Later there is an opening between the 

 two, through which only one nucleus passes from the antheridium, easily 

 recognized by its smaller size ; later, it increases till equal with the 

 female nucleus. The structure of these sexual nuclei and the changes 

 they undergo are fully described. All the antheridial nuclei are similar, 

 and therefore equally able to fertilize the female cell. Changes also 

 take place after fertilization in tbe plasma of the ascogonium and 

 in the neighbouring vegetative cells, which at once become more 

 active. Then follows the degeneration of the other cells of the archi- 



* Zeitschr. Bot., v. (1914) pp. 369-400 (17 figs.). 



