214 



Bmca. 



time goes on, repeated forkings of the twigs from these un- 

 healthy and infested buds, and from successive growths of the 

 same land, give rise to the knotted and confused masses 

 known as Witches' Brooms. Sometimes these make little 

 progress, and the knot merely resembles a rough mass like an 

 old Book's nest thrown down and hanging loosely from the 

 Birch-bough ; sometimes the twigs regain healthy growth, 

 and pushing on for as much as a yard in length form a 

 pendant mass of some beauty, from the delicacy and grace- 

 fulness of the sprays. 



Buds of Birch infested by Gall Mite. 



The infested buds figured above, magnified at fig. 1, maybe 

 distinguished by their spheroidal shape, greater size, and 

 loosely imbricated irregular scales, from the natural growths, 

 which are smooth and lanceolate in general outline. A few 

 months later (about the beginning of February), a touch to 

 one of these distorted buds will often throw off all the diseased 

 scales, and at their bases the coming growth will be found in 

 the numerous minute round buds set close together on the 

 common thickened centre, as shown (magnified) at fig. 2. The 

 growth of the knot from these embryo buds is the work of 

 years ; but whilst the tree is still bare of leaves it may be 

 found in every stage of progress : the shortened shoot beset 

 with swollen buds, as (magnified) at fig. 3 ; the compound 

 form, where many buds have grown close together so as to 

 present a hard cluster, with a few shoots starting from it 

 (figured page 212), and so onwards, till the Witch-knot is fully 

 formed, a mass sometimes more than a yard in diameter. 



In November I found the four-footed Acanis {Pliytoptus) to 

 be present in an active state, amongst the inner scales, in 

 numbers that might be counted by dozens or scores ; and 

 about the beginning of February I found numerous egg-like 

 bodies amongst the diseased leaf-scales, from which Phyto2)ti 

 were shortly after disclosed, occasionally perishing whilst 

 partly excluded from the pellicle, so as to give ample oppor- 

 tunity for examination. These eggs were bluntly ovate (as 



