ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 87 



common. No genetic connection has been certainly established be- 

 tween the two. 



Rosellinia (Rhizoctonia) quercina, a Disease of the Root of the 

 Oak.* — E. Hartig has investigated a disease of young oak-trees, pre- 

 valent in north-west Germany, which he finds to be due to the attacks 

 of this fungus. The mycelium consists of strings, at first white, each 

 of which is composed of a number of interwoven hyphge, making its 

 appearance on the roots, as well as in the surrounding earth and on 

 the surface of the soil. It assumes the three different forms follow- 

 ing : — (1) Chambered sclerotia, when the infection takes place at the 

 apex of the root, before the formation of periderm ; the cortical 

 cells, the walls of which remain, are entirely filled by the polyhedral 

 hyphal cells ; (2) mycelial tubes, which are formed especially where 

 the lateral wall springs, and assume a black colour at the periphery ; 

 protrusions from these tubes penetrate into the sound tissue of the 

 root, especially the cambium, while under favourable circumstances, 

 new strings spread at the same time in the soil ; in times of drought 

 or cold the plant protects itself by a layer of cork from the further 

 attacks of the fungus ; (3) sclerotia, formed out of the strings which 

 run along the surface of the root, single hyphte of which penetrate the 

 cork-cells, rupture them, and produce a pseudo-parenchymatous 

 sclerotium, which persists through the winter or unfavourable season. 



The reproduction of the fungus is effected by means of cylindrical 

 conidia which become abstricted from verticillate branches of the 

 mycelium on the surface of the soil ; as also by perithecia, the sexual 

 origin of which is highly probable. From the form of the peritliecia 

 and spores it belongs to the genus Bosellinia de Not. ; before the dis- 

 covery of the perithecia it was referred to Bhizodonia. The injury 

 effected by this parasite is very considerable. 



Olpidiopsis, the Parasite of Saprolegnia.f — The spiny spherical 

 bodies {Stachelkugeln) commonly found in connection with the tubu- 

 lar cells of Saprolegnia and Aclilya, have often been described, and 

 their true nature much contested. Nageli first discovered on the 

 swollen filaments of Aclilya proUfera elongated cells which penetrate 

 the filaments by means of a short tube, and from which escape ex- 

 tremely small motile bodies. These he considered to be non-sexual 

 organs of reproduction. Cienkowski observed the presence of spiny 

 bodies in company with the smooth ones, and came to the same con- 

 clusion respecting their nature. A. Braun regarded them as a parasite 

 on the Saprolegnia, describing them under the name Chytridium Sapro- 

 legnicB, as the representative of a new genus. The smooth cells he 

 described as sporangia, and their motile contents as swarm-spores. 

 Pringsheim, on the other hand, to explain what would otherwise be a 

 parthenogenetic development of oospores (oosjierms) in Saprolegnia, 

 regarded the smooth bodies as male organs, the motile contents as 

 antherozoids ; but he offered no explanation of the spiued bodies. 

 Cornu, again, gave a decided judgment in favour of the parasitic 



♦ Unters. forstbot. Inst. Munchen, 1880, p. 1. 



t Bot. Ztg., xxxviii. (1880) pp. 689-96, 705-11, 721-6 (1 pi.). 



