767 



that other varieties may be found in other countries and it is beheved 

 that such a variety, differing but little from P. jjervastatrix, occurs in 

 the province of No vara. The supposed existence of biological races 

 may be of great practical importance and may be connected with the 

 enormous differences between the results obtained in the fight against 

 this pest. The worst ravages have occurred in regions where vine- 

 yards are specialised, tiie least, in those where the vines are kept high, 

 planted in rows with intervening plots cultivated with herbaceous 

 crops, or w^here they are trained on trees and at a good distance apart, 

 etc. It has also been proved that the damage makes less rapid progress 

 among vines in which the aerial and consequently also the underground 

 portions, are well developed. Other factors have to be considered, 

 such as the division of the property and the share system which 

 exclude, more or less completely, extraneous factors capable of spread- 

 ing Phylloxera. All these circumstances have their value, and the 

 intensity and accuracy of methods with which the control of Phylloxera 

 has been conducted, also count for something, but they still appear 

 insufficient to give a complete explanation of all the phenomena under 

 discussion. Something is still wanting, and this is contained in the 

 following dilemma : — Either the Phylloxera becomes weakened or in 

 certain localities becomes benign in response to its environment, or 

 there are benign and malignant races of this pest. This seems to be 

 the only really important point in the biology of Phylloxera which still 

 requires elucidation, and experiments have already been begun with 

 this object. This very important and detailed paper should be 

 consulted in the original by all interested. 



KoLMODiN (G.). Grantorkan och barkborren. [The dying of spruce 

 and the spruce bark-beetle, /^;.s- typographus.] — Norrlands Skogs- 

 vdrdsforbunds Tidskrift, 19f5, no. 3, 28 pp., 14 figs. 



Most of the observations embodied in this paper were made in the forest 

 reserve at Orsa in Dalecarlia, Sweden, which covers about 14,000 acres. 

 Experiments showed that low temperatures do not affect the beetles 

 beyond prolonging the life-cycle. In order to ascertain whether the 

 beetles were the primary cause of the dying of the spruces, circulars 

 were sent to 20 interested persons requesting them to state their 

 experiences on this point. Of these, five answered that they con- 

 sidered the beetle the primary cause, seven did not consider this to be 

 the case, and the rest had not formed any opinion. This diversity 

 of opinion probably depends partly on the different behaviour of the 

 beetles under different circumstances, and partly on the fact that the 

 attacks are often discovered so late that the problem cannot be 

 investigated. Both in 1913 and 1914 the bark-beetle has undoubtedly 

 been the primary cause of the dying of the spruces. In many instances 

 it attacked perfectly healthy trees, including single ones, as well as 

 those in groups. In Orsa and Hamra, at least one thousand trees 

 were attacked one after the other. The bark-beetles do not, however, 

 cause primary damage to spruces unless they are present in com- 

 paratively large numbers, sufficient to attack healthy trees success- 

 fully. The author found several spruces which had been attacked by 

 the beetles, but shortly afterwards had been abandoned by them, 



