58 DISEASES OF TREES 



In the tissues of the host-plant, though occasionally outside 

 of it, female sexual organs (oogonia) originate on the mycelium, 

 and during fertilization the male sexual organs, called pol- 

 linodia or antheridial branches, are brought into contact with 

 these oogonia. The antheridia send a minute process (the fer- 

 tilizing-tube) into the interior of the oogonium, which is fer- 

 tilized by its protoplasm receiving a small portion of the con- 

 tents of the antheridium. This gives rise to the formation of 

 the egg-spore (oospore), which is provided with a thick cell-wall. 



While the gonidia, being easily detached and carried by 

 wind or animals, provide for the rapid distribution of the 

 parasite during summer, the oospores reach the ground in 

 the dead and decaying parts of plants. There they pass the 

 winter indeed, in such a position they may remain alive for a 

 number of years after which they either germinate directly, or 

 first of all produce sporangia with zoogonidia.* 



PHYTOPHTHORA OMNIVORA (SYN., PHYTOPHTHORA FAGI, 

 AND PERONOSPORA SEMPERVIVl). 1 



The disease caused by this parasite was noticed in forestal 

 publications over a hundred years ago as " the disease of seedling 

 beeches," and cannot be unknown to any forester employed in 

 beech woods. When seedlings are abundant after a rich seed- 

 year the disease is to be met with over the whole of Germany, 

 and the more plentifully the wetter the months of May and June. 

 The fungus also attacks other broad-leafed trees, e.g. Acer, 

 Fraxinus, Robinia, as also herbaceous plants such as Fagopyrum, 

 Clarkia, Sempervivum, &c. The parasite is equally widely dis- 



1 I described this parasite in 1875 in the Zeitschrift fur Forst- und Jagd- 

 wesen, pp. 117 123, under the name of P. fagi. A detailed account of the 

 history of its development, and of the disease to which it gives rise, along 

 with a plate, was contributed by me to the Untersuchungen aus dem forst- 

 botanischen Institut, 1880, pp. 3 57. In 1875 that is to say, simultaneously 

 with me Schenk described this fungus under the name of P. sempervivi. 

 In order to settle the question of priority De Bary selected the name 

 Phytopkthora ornnivora (Beilrage zur Morph. und Phys. der Pilze, 1881, 



p. 22). 



* [For an account of the Phycomycetes peculiar to Britain the reader 

 may be referred to Massee's British Fungi (Reeve & Co., 1891). ED.] 



