Page:Popular Science Monthly Volume 5.djvu/722

702 was attained, so that there was only a momentary exposure to the temperatures about to be cited. Of those which had been exposed to 190° Fahr., many did not germinate; still fewer of the seeds that had been exposed to 201° produced young plants, while, of those heated to 212, not one germinated. After the young plants (developed from seeds heated to lower temperatures) had grown for thirteen days, their capability of resisting heat was tested in the manner described, and with this result. Those whose roots had been momentarily exposed to 156° continued to live after they had been replanted, while those whose roots had been exposed to 167° and upward speedily dried up and perished, although, like the others, they had been replanted in carefully-watered earth.

These were the only complete experiments made by Spallanzani with plants and their seeds; but many other kinds of seeds only, including those of the broad-bean, barley, kidney-bean, maize, vetch, spinach, beet-root, turnip, and mallow, were also exposed to the influence of heat while packed in dry sand. Although this method is less exact and trustworthy, and is one with which we are not now concerned, still it may be stated that only four of the numerous seeds with which experiment was made after this fashion survived their brief exposure in the dry state to the temperature of 212°; all the others failed to germinate.

The abbé's researches, therefore, taught him three things: 1. That eggs can endure a decidedly higher degree of heat than that proving fatal to animals of the kind from which they have been derived; 2. That an analogous difference exists between seeds and plants in respect to their capacity of withstanding the action of heat; and, 3. That seeds and plants can resist higher grades of heat than eggs and animals respectively.

After calling attention to these conclusions, Spallanzani said (p. 64): "Of course I am far from pretending to explain these results; I know the difficulty of the undertaking, and will only venture a few conjectures, at most, letting them go for what they are worth, and leaving every one free to think as he pleases." As his conjectures, however, cannot be much improved upon at the present day, I may as well call the reader's attention to them by briefly pointing out their nature.

At the first glance, the abbé says, the superior power of resisting heat displayed by eggs and seeds, as compared with animals and plants, might be supposed to be due to the latter feeling the effects of heat more rapidly, owing to their being free from those envelopes which inclose the egg or the seed. But the weight of this supposed reason soon disappears, in the case of eggs at all events. Looking to the thinness of their investing membrane, this supposition, as Spallanzani says, "seems very improbable indeed, when we consider how easily and how rapidly fire penetrates so thin a layer of matter." He