212 



BIRCH. 



BIRCH. 



Gall Mite, rhi/toptiis (? sp.) 



Gall Mite of the Birch, mag., nat. length two-hundredths of an inch ; egg, also 

 greatly magnified ; deformed shoot (smaller than life). 



The Witch -knot, or great bunch of twigs looking Hke a large 

 bird's nest fallen at random amongst the branches of the 

 Birch, may frequently be noticed ; and amongst the various 

 forms of galls caused by Phytopti this peculiar growth of twigs 

 in the Birch tree is of some interest, from the attack of the Gall 

 Mites producing an increased development of woody growth 

 from the infested buds, instead of — as is usually the case — leaf- 

 galls, or diseased leaf-buds alone. 



As far as I am aware up to 1876 this special attack had 

 not been studied, and the following observations on the origin 

 and progress of this diseased formation were taken by myself 

 in part from so-called "Witches' Brooms " growing in Saver- 

 nake Forest, near Marlborough, and also from growths on 

 Birch trees planted by the roadside at Spring Grove, near 

 Isleworth, which (probably from the unsuitableness of the 

 situation) suffered so much from Gall Mite that, whilst 

 resident there in 1876 and 1877, 1 was able to trace the effects 

 of the infestation from the beginning.* 



The Plujtojytns causing the diseased growth is greyish- 

 white, cylindrical, and rarely exceeding one two-hundredth 

 of an inch in length, and a quarter of that measure at its 



* In the 1st Edition of my ' Manual,' I gave a short note regarding this attack, 

 which was all that space would permit, but now, as the infestation is of some 

 interest, I reprint by permission most of the information, together with the 

 figures drawn by myself from life, from my paper given in the 'Entomologist,' 

 vol. X., 1877 (No. 1G7). Messrs. Simpkin & Co., London. 



