AMENTIFER^ 



135 



and is enclosed in a scaly involucre called a cup. 

 Acorns are very bitter, especially when ripe, but 

 are much used for feeding pigs. Some of the 

 South European species of oak, however, bear 

 sweet instead of bitter acorns. Oak-bark has long 

 been used for tanning leather ; cork is obtained 

 from the bark of some species ; and ink is manu- 

 factured from the galls which grow on others. 



Hundreds of different species of insects feed on, 

 or are associated with, the Oak. Among beetles 

 the large Stag-Beetle (Lucanus cervus) lives as a 

 white grub in the wood of the Oak and other 

 trees. It varies much in size : some of the large 

 males are nearly 3 inches long, while others are 

 much smaller, and with much smaller mandibles. 

 The mandibles of the females are small, and 

 not branched, but nip severely. The beetles are 

 blackish, with reddish-brown wing-cases. These 

 beetles feed on the sap of trees ; their grubs, as 

 already mentioned, on the solid wood of trees. 

 The white grubs of different species of Cockchafers 

 (brown or grey beetles with the end of the antennae 

 formed of expanding laminae like a fan) do much 



harm by feeding on the roots of grasses; but the 

 beetles themselves, when abundant, are almost 

 equally injurious to trees, flying round them in 

 the evening, and sometimes, when excessively 

 numerous, devouring the leaves of whole forests, 

 almost like a swarm of locusts. 



Two very interesting butterflies, both of a prevail- 

 ingly blue or purple colour, are associated with the 

 Oak. The Purple Hairstreak (Zephyrus Qiiercus) 

 is found commonly flying about Oaks in summer. 

 It has a short tail on the hindwings; and the under- 

 surface is bluish grey. It measures an inch and 

 a half across the wings. The caterpillar feeds on 

 Oak ; it is of a yellowish grey with yellow spots, 

 and woodlouse-shaped. The Purple Emperor 

 (Apatura Iris) is a much larger butterfly, measur- 

 ing 3 inches across the wings, which are brown, 

 banded with white, and marked with a black spot 

 in a yellow ring near the hinder angle of the hind- 

 wings. The male is magnificently shot with purple. 

 The green caterpillar, with two horns on its head, 

 lives on Sallow ; but the butterflies, especially the 

 males, are fond of flying round the summits of the 



