252 



(8) Laburnum vulgare and L. aipinum. — The 



-Laburnum is mentioned by Giissow (12j, 



Pickering 



common 



and 



(8), 



Brooks (9), as having- suffered from Silver leaf disease. Apart 





L 



Text fig. 



/. 



Longitudinal section through the wood of a shoot of. 



Kibes cerenm. 



from the genus Vrunus I have noticed no more extensive destruc- 

 tion on any other ornamental tree or shrub as a result of Stereum 

 purpureuni than on Laburnum alpinum. Judging from the 

 damage caused during 1918 in, the surburban district of London, 



s 



to 25 



up to zo per 

 fructifications 



cent, of the trees 



autumn and 



where, in certain localitie 



developed S. purpureum fructifications during 

 winter, it is highly probable that unless drastic measures are 

 taken the cultivation of Laburnum alpinum will become 

 impossible. So far I have only met one case of a living tree of 

 Laburnum vulgare bearing S. purpureum fructifications. A living 

 side-branch of L. vulgare about four years old showed discolora- 

 tion in the wood, a discoloration occupying about 100° of the 

 circumference, but the extent gradually diminished upwards in 

 the four and three vpnr old wnnrl. On rpnchinjy the 



year oia wood. On reaching 

 two-year-old branches it was confined to the cambial region and 

 to about one-third of the circumference, whereas in the one-year- 



i . 





i l 5b 



*^> 



f W^ 1 













• _ 





y 



s 





* 



* * 







Text fig. 8. — Eadial longitudinal section of the xylem vessels of Laburnum 



vulgare showing deep discoloration and abundant hyphae. 



