THE LARCH. 227 
or early in summer, such as that which occurred in May 1861. 
On the 10th of that month the thermometer exposed reached 
80°, while on the following night or morning of. the 11th it 
descended to 19°, being 13° below the freezing point. This 
had a very damaging effect on the larch plantations through- 
out the country. Such a visitation is usually followed by a 
severe attack of the Coccus laricis, which multiplies with 
amazing rapidity,’ and not unfrequently overspreads the sur- 
face of the young branches, consuming every leaf as it emerges 
from the bud, and several weeks sometimes elapse before the 
tree is able to renew its foliage. The sap appears to exude 
by the numerous perforations, and to form a black coating 
resembling the effects of smoke, and the top shoots of such 
trees are uniformly short and feeble. 
This state of affairs shows the advantage of a northern 
aspect and a cool situation, where the tree may not come 
early into leaf. There are some dry, gravelly knolls exposed 
to sunshine, which early in spring imbibe heat, raising the 
temperature of the soil, and expanding the leaf very early. 
In such soil the larch is a very precarious crop. Ample 
space for the tree increases the extent of foliage, and is 
always favourable to the tree when attacked. The Coccus is 
least injurious where there is a free circulation of the atmo- 
sphere, and where the plantation does not consist purely of 
larches. Plantations formed of plants free from disease, and 
thoroughly isolated from infected trees, have been known to 
1 Respecting some kinds of this insect, Curtis states the startling fact, 
that the spring broods are all females, and do not require any intercourse of 
the sexes to render them prolific. They are pregnant at their birth, and if the 
nit (as it is termed) brought forth by the fly in the spring be taken and kept 
entirely excluded from its companions, it will be able to produce young ; and 
if one of these be treated with the same precaution, it will yet be found to 
retain the same powers of conception; and thus one may proceed for twenty 
or thirty generations. This will explain their otherwise marvellous multipli- 
cation; and the warmer the weather the more rapidly families increase; so 
that it has been calculated by an eminent naturalist, that from one egg 
729,000,000 of plant-lice might be produced in seven generations ; admitting 
forty to be the maximum, and twenty the minimum, the average would be 
thirty, and the generations from the spring to the autumn amount from 
sixteen to twenty, or upwards. 
