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IX. — Researches into the Nature of the Potato- fungus — Phyto- 
phthora infestans. By Professor A. de Bary, of the Univer- 
sity of Strasbourg. 
Introduction. 
Previous to my undertaking, at the request of the Royal Agri- 
cultural Society, the task of endeavouring to extend our know- 
ledge of the life-history of the potato-fungus, I had devoted a 
long series of researches to this subject. Although I assume 
that those researches, so far as they have been published, are 
known — and, in fact, I must do so for the sake of avoiding too 
great minuteness of detail — yet a short resume appears indis- 
pensable ; and I will give it by way of introduction, referring, 
at the same time, to the existing literature of the subject.* 
1. The potato-fungus is usually classed with a small family 
of parasitic fungi, which since 1863 has been known as the 
Peronosporeae. 
Taking first the purely morphological peculiarities of these 
fungi, without regard to their immediate adaptation to the 
medium in which they grow, we find in the first place that the 
growing plant {thallus, mycelium) consists of densely ramified 
tubes ; these are full of protoplasm and continuous, or without 
septa, except that some individuals, especially when they are old, 
have irregular septa. Some small branches of the mycelium are 
specially developed as organs for attachment and as suckers ; 
others produce the organs of reproduction. One set of these last 
bear non-sexual cells {conidia\ and are therefore called " conidia- 
bearing " (conidiophores) ; others, which mark the complete de- 
velopment, form at their tips the sexual organs : these are (first) 
the bladder-shaped female cells (pogonia'), from the protoplasm 
of which a thick-walled oospore is produced, after fertilisation by 
(second) the small male cells (the antheridia). From the ger- 
minating oospore springs directly or indirectly one or more new 
rudimentary mycelium threads (" gferm-tubes "), with which the 
process of development just sketched begins afresh. I have here 
employed for the sexual organs and the structures developed 
from them the terms which at present are most in use, and will 
continue to do so in the following pages, though other terms 
might be employed which are more correct. The use and 
explanation of these, however, would lead me beyond my present 
purpose. 
* Eecherches sur le developpement de quelques cliampignons parasites.' Aym. 
Sc. Nat. 4°" serie, t. xx. ' Die gegenwiirtig herrschende Kartoffelkrankeit. 
Leipzig, 1861. ' Zur Kenntniss der Peronosporen,' De Bary and Woronin, Beitr. 
X. Morphol, &c. d. Pike, Heft 2, p. 35. 
