Entwicklungsgeschichte 
175 
Annahme, daß es sich um Microsphaera quercina (Schw.) Burrill, eine 
der Formen der SALMONschen Sammelspezies M. Alni handle. Diese 
Vermutung findet nun ihre Bestätigung dadurch, daß einer der Verf. 
vorliegenden Artikels am 30. Dez. 1911 in Cavillargues (Gard) auf Quer eus 
sessiliflora Perithecien auffand, welche mit Exemplaren der genannten 
Spezies aus Amerika völlig übereinstimmen. Die Verff. glauben aber 
nicht, daß die Epidemie der letzten Jahre auf eine neuerdings erfolgte 
Einschleppung aus Amerika zurückzuführen sei, sondern daß der Pilz 
in Europa schon lange mehr vereinzelt existiere, aber dann in den letzten 
Jahren infolge leichter Veränderungen der äußeren Bedingungen eine 
starke Entwicklung erfahren habe. Die Entstehung der Perithecien, 
welche die Verff. beschreiben, kann ebenfalls auf besondere Verhältnisse 
der betreffenden Eichenblätter und auf die exceptionellen Witterungs¬ 
verhältnisse des Jahres 1911 zurückgeführt werden. Ed. Fischer. 
BÀRRETT. J. T., Development and sexuality of some species of 
Olpidiopsis (Cornu) Fischer. (Ann. Bot, 1912, 26, 209—238, 
4 plates.) 
The author worked with three species of Olpidiopsis, O. vexans 
nov. sp. (= O. Saprolegniae A. Fischer), O. luxurious nov. sp. and 
O. Saprolegniae Cornu. All three are described, the first two being 
given latin diagnoses. 
Barrett summarises his work thus: The zoospores of all three 
species of Olpidiopsis studied possess two cilia of equal length attached 
at or near the anterior end of the elongated body. They have two motile 
stages separated by a brief period of rest, which suggests a primitive 
type of diplanetism. The individuality of the zoospore after entrance into 
the host is maintained throughout its development, there being no plas¬ 
modium formed. Aside from a slight amoeboid movement immediately 
after entrance the parasite does not undergo any noticeable changes in 
form. 
Segmentation of the sporangial contents has, at least partially, taken 
place before the entrance of the sporangium into a period of rest, when 
such occurs, and is apparently simultaneous throughout. The zoospores 
on escaping contain vacuoles. 
True sexuality probably exists, and takes place by the fusion of two 
sexually differentiated individuals and the subsequent passage of the 
protoplasm of the smaller, maler, into the larger, female, cell. This is 
followed by a supposed fusion of nuclei. 
Both sexual and asexual reproductive bodies develop rather rapidly 
from a uninucleate to a multinucleate condition. The oospore is likewise 
multinucleate. External conditions play a great part in the determination 
of sex in these organisms. This fact adds evidence to the doctrine that 
sex in many plants is determinable by external or nutritive conditions. 
Nuclear division is mitotic with the spindle intranuclear. The 
number of chromosomes is approximately six. No centrosomes nor any 
other indication of nuclear polarity wer observed. 
These forms seem to be primitive sexual organisms of the Oomycete 
type. The influence of external conditions on the development of the 
sexual stage, the mode of fertilisation, the unequal size of the two gametes, 
