point. On the other hand, some of the impure bitumens soften or fuse at a low temperature and contain a good deal of enclosed water. When this water is heated at a relatively low temperature, it is expelled and makes the mixture look as if it were boiling. The apparent difference in the method of preparing the material at the time of Theophrastus and at later times also indicates that it was an impure bitumen. Posidonius366 states that before application it was mixed with oil, which would be necessary if a viscous material were to be formed out of glance pitch. Dioscorides367 also mentions its solubility in oil, though he does not specifically state that it was dissolved in oil before it was applied to the vines. Theophrastus, it will be noted, says nothing about adding oil. Possibly he was unaware that oil was mixed with it, or possibly when he refers to a boiling process, he means that the material was dissolved in hot oil. On the other hand, with some impure bitumens no addition of oil would have been necessary to obtain a preparation suitable for vines. Therefore, it is not unlikely that the earth here mentioned by Theophrastus was a bituminous clay or sand, not the pure bitumen which appears to have been used in later times.
Though die main reason for applying a bituminous preparation to the vines seems to have been to catch harmful insects on its sticky surface, it is also possible that it had an important and perhaps unrecognized virtue as a fungicide.
50. It would also be possible to determine the differences that are naturally adapted for causing earth to turn into stone; for those that are due to locality, which cause different \inds of savors, have their own peculiar nature, li\e those which affect the savors of plants. But it would be best to list them according to their colors.
In his Causes of Plants™* Theophrastus makes a comparison between the juices or flavors in plants and in earths. He seems to imply here that differences in environment, which certainly cause differences in plants, may also cause differences in the properties of earths, and that it might be possible to classify earths on such
3ββ According to Strabo, VII, 5, 8. 8e7V, 180 (Wellmann ed., V, 160).
868 VI, 3.
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