ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 335 



Fungi. 

 (By A. LoERAiN Smith, F.L.S.) 



Infection Experiments with Peronospora.* — G. von IstvanffiandG. 

 Pcilinkas undertook these experiments in order to understand more fully 

 the biology of the parasite and its relation to the vine. They made 

 constant observations on the times of infection and on the spread of the 

 fungus in the open. In some cases the infection was successful, in others 

 not, but the variation might depend on the host and on its moisture- 

 content at the time. The more water there is in the cells of the plant, 

 the more liable it is to attack. The development of the fungus depends 

 also to a large extent on sudden cooling of the air, especially when 

 accompanied by rain or dew ; there is then little transpiration and the 

 cells are turgid with sap. Any influences that aid in reducing the water 

 content of the host cells, tend to ward off infection. 



Development and Sexuality of some Species of Olpidiopsis.f — The 

 species of this genus are parasitic on various Piiycomycetes or on 

 filamentous green algae. The genus is interesting as being a member of 

 the Chytridiales in which sexuality is supposed to occur. J. I. Barret 

 has made a thorough study of three species collected in the vicinity of 

 Ithaca, two of them parasitic on SaproJegnia, the third on Aphanomyces. 

 As a result of his work he finds that the zoospores are biciliate in all 

 three species, and have two motile stages, separated by a brief period of 

 rest, which suggests a primitive type of diplanetism. There is no 

 Plasmodium formed after the zoospore alights on the host ; but there is 

 a slight amoeboid movement after entrance, followed by a rounding up 

 of the zoospore body and the formation of a wall. After a short period 

 of rest a tube is produced which penetrates the hypha of the host and 

 the contents of the zoospores pass into the host. The parasite grows at 

 the expense of the host protoplasm, and becomes surrounded by a wall 

 forming a sporangium. Segmentation of the sporangial contents takes 

 place partially before the resting stage of the sporangium. The zoospores, 

 on escaping, contain vacuoles. 



Sexual spores are developed in the same position as the sporangia. 

 They can be detected by the darker and more dense condition of the 

 protoplasm, especially of the larger (the female) cell ; fusion takes place 

 by the passage of the contents of the smaller male cell into the larger, 

 followed by a supposed fusion of nuclei. A multinucleate condition 

 follows. The oospore is also multinucleate. 



External conditions play a great part in the determination of sex. 

 Nuclear division is mitotic with the spindle intranuclear. There are 

 about six chromosomes. No centrosomes nor other indication of polarity 

 was observed. The writer concludes that the fusion of two unequal 

 gametes constitutes a case of primitive sexuality of the oomycete type. 



Germination of the Conidia of Plasmopara viticola.| — In a drop 

 of water at 15^ C, L, Ravaz and G. Verge watched, in three-quarters of 



* Centralbl. Bakt., xxxii. (1912) pp. 551-64. 

 t Ann. of Bot., xxvi. (iyi2) pp. 209-38 (4 pis.). 

 J Comptes Rendus, cliii. (1911) pp. 1502-4. 



