288 HOW TO GROW GOOD TIMBER. 



found in the interior of its cell : in other words, the excrement would 

 be there, for there is no outlet, and the lacteals or absorbent vessels 

 of the gall could not take it up. I therefore think that the creature 

 feeds entirely on the sap of the tree — an elaborate food fit for it 

 without the need of mastication. This explains how it happens that 

 the galls of commerce, with the insects in them, are so much better 

 and dearer than those from which the cynips has escaped ; in a word, 

 the tannic acid is more abundant. 



It has been before observed, that there are two broods of the insect 

 in a season ; thus, those which do not emerge from the gall in Sep- 

 tember remain on till the following April or May. This is a wise 

 provision of nature for continuing the species, should anything befall 

 the autumn brood ; and it is the more deserving of notice, because the 

 gall-producing cynips has a deadly enemy which accompanies or 

 follows it in its flight from bud to bud, and deposits an egg wherever 

 it finds the egg of the cynips. Here, as soon as the cynips larva is 

 hatched, the larva of the parasite is hatched also ; forthwith the latter 

 proceeds to eat a hole in the skin of the rightful occupant of the 

 nidus, and the two larva? go on growing together till the cynips is 

 ready to assume the pupal state ; then the parasite cuts the vital 

 thread of the cynips, and uses its skin for a pupal envelope for itself ; 

 and thus, instead of the gall-fly emerging into day, a beautiful green 

 insect makes its appearance on the stage of life. I had the pleasure 

 of first discovering this parasite while engaged in studying the cynips; 

 it belongs to the genus Callimone, and from the fact of having dis- 

 covered it in Devonshire, I gave it the name of Callimone Devoniensis. 

 It is one of the handsomest of our British insects ; its costume a 

 brilliant green, shot with gold ; the abdominal segments green, gold, 

 and purj)le ; legs yellow ; tarsi reddish ; and it has four beautiful 

 transparent and iridescent wings. 



It has been stated that oak-galls are produced at the expense of 

 acorns. From this view my experience leads me to dissent. In 

 exceptional instances it may have been the case ; but as a rule the 

 cynips confines its attacks to young trees and young growths in hedges, 

 within a range of ten or twelve feet from the ground, and the nearer 

 the ground the more numerous the galls. Young trees which have not 

 attained a greater height than that I have indicated suffer so much 

 that many of them can scarcely make headway against their foe ; and 

 in several nurseries I have visited, where it might be expected that 



