Il6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



doH's-house-rookery, and dozens of examples of the growth occur 

 on single trees. In the spring the fresh growths are greenish in 

 colour, like the foliage, and as they dry up and wither they 

 change to brownish, ending by becoming almost black in the 

 rather smoky atmosphere. They persist and remain on the trees 

 throughout the winter, conspicuous and eye-arresting objects. 

 They occur on at least four different species of willows, namely, 

 Saiix babylonica, S. alba, S. fragilis, and S. vitellina. 



It is apparently a case of phyllody ; and Mr N. E. Brown of 

 Kew Gardens, to whom I submitted specimens, writes that the 

 branches show " modified female catkins, in which the female 

 flowers are transformed into a more or less leafy state, v/here 

 each flower becomes an aborted leafy shoot. Some of the carpels 

 are modified into an expanded leaf at the base of a partly 

 enclosed rudimentary leafy axis, and some are much enlarged 

 carpels, containing a small leafy axis bearing two or three minute 

 leaves inside. There is no disease apparent. It is a very 

 interesting modification." At Mr Brown's request, further 

 specimens were sent to the Director at Kew for the herbarium 

 there, and a later report from this authority says — "The hyper- 

 trophy of the willow catkins received is possibly caused by a 

 mite, as these creatures were found on the older diseased pieces. 

 In the older stages the twigs have become greatly swollen, and 

 adventitious flowers formed in great number from the tissues." 



This still leaves the cause of the malformation an open 

 question, but it seems probable that it is due to a gall-mite of 

 the genus Eriophyes. In the Forestry Museum, Kew Gardens, 

 there is a specimen labelled Eriophyes fragilis, looking very like 

 the Hampstead growths. I am told that another species, E. 

 iri-radiatus, attacks both S. alba and ^. fragilis, and that E. rudis 

 has a partiality for birches. Messrs Elwes and Henry ^ refer to 

 *' Witch's Broom " on the white willow {S. alba), apparently 

 formed by irritation set up by Eriophyes salicis, but the description 

 given by them of the resultant growth differs from what is found 

 on the Hampstead trees. 



As so little seems to be known about these abnormalities on 

 willows, any further information would be useful. 



Hugh Boyd Watt. 



^ Trees of Great Britain and Ireland, vol. vii. p. 1 76 1. 



