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Now, the essential cause of the potato disease is perfectly well understood. It is parasitical, the parasite being a fungus, the Peronospora infestans, which grows at the expense of the leaves, stems, and tubers of the plant until it destroys their vitality.
And yet this "Monad" can be traced, step by step, through the series of metamorphoses which I have described, until it assumes the features of an organism, which is as much a plant as is an oak or an elm. Moreover, it would be possible to pursue the analogy farther. Under certain circumstances, a process of conjugation takes place in the Peronospora.
Murray, "I instituted the following experiments, with the object of determining the mode of diffusion of the conidia of Peronospora infestans.
It was a progress northward.... This plant, the Peronospora infestans, will only grow on the Solanum tuberosum, that is, the cultivated potato.... Just as plants of higher organization choose their soils, some growing in the water and some on land, so the Peronospora infestans chooses its host plant; and its soil is this species, the Solatium tuberosum.
"I determined the nature of the conidia by comparing them with authentic conidia directly removed from diseased plants; by there being attached to some of them portions of the characteristic conidiaphores; and by cultivating them in a moist chamber, the result of which was, that five conidia, not having been immersed in the glycerine, retained their vitality, which they showed by bursting and producing zoospores in the manner characteristic of Peronospora infestans."
Like many other Fungi, the Peronosporoe are parasitic upon other plants; and this particular Peronospora happens to have attained much notoriety and political importance, in a way not without a parallel in the career of notorious politicians, namely, by reason of the frightful mischief it has done to mankind.
Undoubtedly it is possible to bring forward very strong arguments in favour of regarding Heteromita as a plant. For example, there is a Fungus, an obscure and almost microscopic mould, termed Peronospora infestans.
But it may be said that the Peronospora is, after all, a questionable sort of plant; that it seems to be wanting in the manufacturing power, selected as the main distinctive character of vegetable life; or, at any rate, that there is no proof that it does not get its protein matter ready made from the potato plant. Let us, therefore, take a case which is not open to these objections.
Close on the heels, or rather the wings, of the Anthomyia Ceparum, fell the Peronospora Schleideniana. "It isn't often it happens," said ARPACHSHAD, rubbing his hands gleefully; "but, when you get one on the top of t'other, you don't look for much crop in that particular year." A Hand-book to Honesty. SCENE I. Apartment of innocent but temporarily impecunious person.
The singular circumstance observed by Meyer, that the Torula of yeast, though an indubitable plant, still flourishes most vigorously when supplied with the complex nitrogenous substance, pepsin; the probability that the Peronospora is nourished directly by the protoplasm of the potato-plant; and the wonderful facts which have recently been brought to light respecting insectivorous plants, all favour this view; and tend to the conclusion that the difference between animal and plant is one of degree rather than of kind, and that the problem whether, in a given case, an organism is an animal or a plant, may be essentially insoluble.
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