“What are oak-galls, Miss Harson?” asked Malcolm.  “Are they the same as oak-apples?”

“Not quite the same,” was the reply, although both are produced by the same insect.  This is what one of our English books says of them:  ’When the acorn itself is wounded, it becomes a kind of monstrosity, and remains on the stalk like an irregularly-shaped ball.  It is called a “nut-gall,” and is found principally on a small oak, a native of the southern and central parts of Europe.  All these oak-apples and nut-galls are of importance, but the latter more especially, and they form an important article of commerce.  A substance called “gallic acid” resides in the oak; and when the puncture is made by the cynips, it flows in great abundance to the wound.  Gallic acid is one of the ingredients used in dyeing stuffs and cloths, and therefore the supply yielded by the nut-gall is highly welcome.  The nut-galls are carefully collected from the small oak on which they are found, the Pyreneean oak.  It is easily known by the dense covering of down on the young leaves, that appear some weeks later than the leaves of the common oak.  The galls are pounded and boiled, and into the infusion thus made the stuffs about to be dyed are dipped,’”

“I should think,” said Clara, “that people would plant oak trees everywhere, when they are so useful.  Is anything done with the bark?”

“Yes,” said her governess; “the bark, which is very rough, is valuable for tanning leather and for medicine.  The element which has the effect of turning raw hide or skin into leather is called tannin; it is also found in the bark of some other trees and in tropical plants.”

“Didn’t people use to worship oak trees,” asked Malcolm—­“people who lived ever so long ago?”

“You are thinking of the Druids, who lived in old times in Britain and Gaul,” replied Miss Harson, “and whose strange heathen rites were practiced in oak-groves; and they really did consider the tree sacred.  These Druids have left their traces in some parts of England and France in rows of huge stones set upright; and wherever an immense stone was found lying on two others, in the shape of a table, there had been a Druid altar, where the priest offered sacrifices, often of human beings.  So horrible may be a so-called religion that men themselves devise, and that has not come from the true God.

[Illustration:  DRUIDIC SACRIFICE.]

“It was an article in the Druids’ creed, and one to which they strictly adhered, that no temple with a covered roof was to be built in honor of the gods.  All the places appointed for public worship were in the open air, and generally on some eminence from which the moon and stars might be observed; for to the heavenly bodies much adoration was offered.  But to afford shelter from wind or rain, and also to ensure privacy and shut out all external objects, the place fixed upon, either for teaching their disciples