Or FRUIT TREES. 89 



(ant ; in rass land from one to four inches deep, and 

 in ploughed land not more than to the depth of seven 

 or eight inches. He has also ascertained that a part 

 of the canker moths iise in the autumn and deposit 

 their eggs. They are such as were an inch or two 

 below the surface 5 those which lie deeper are not af 

 focted by the transient changes of the atmosphere in 

 November, and do not rise till spring. The chrysalis 

 state comes in twenty-four hours after the larvae has 

 penetrated the earth, and it appears that the insects 

 are soon perfect, since a course of warm weather has 

 been found to raise some of them from the earth in 

 November. Those which rise in November are not 

 very numerous, compared with those which rise in 

 the spring, but being very prolifick are exceedingly 

 injurious, if no means are taken to prevent their as- 

 cending the trees ; as the winter's frost does not kill 

 the eggs. The warmth of the season at the time of 

 the descent into the soil is favourable to the perfect 

 development of the insect in the chrysalis, particular- 

 ly those which are nearest the surface, while those at 

 the depth of six or seven inches are longer in coming 

 to maturity. The first are perfect in September, and 

 require only to be excited to burst from their confine* 

 merit; but they cannot be excited until they have 

 passed through a degree of cold sufficient to make 

 them sensible of the mild temperature of the atmos- 

 phere which occurs in November. The excitability 

 of such as lie deeper, and are not accessible by cold till 

 a later period of the season, is not so soon accumulat- 

 ed, nor are they sensible of slight changes of temper- 

 ature, which affect only the surface ; they, therefore, 

 do not leave the earth till the spring, when the warmth 

 of the air is longer continued, and penetrates to the 

 depth at which they lie. To prevent the dreadful 

 ravages of the canker worm, the great object is to 

 keep the female from ascending the trees. For this 



