390 PROF. J. PERCIVAL ON “ SILVER-LEAF ”’ DISEASE. 
Figs. 5, 6. Bornean specimen, Haviland, 2015. 
Fig. 5. Pitcher removed from the branch. 
Fig. 6. Pitcher shown in fig. 5, with portion of wall removed. 
Figs. 7, 8. D. complex. 
Fig. 7. Pitcher removed from the branch. 
Fig. 8. Pitcher shown in fig. 7, with portion of wall removed. 
Figs. 9, 10. Bornean specimen, Motley, 525. 
Fig. 9. Pitcher with portion of wall removed. 
Fig. 10. Lobe of inner pitcher (enlarged). 
Fig. 11 (after Beccari). A portion of a longitudinal section through the 
pitcher of D. Rufflesiana, showing the inflexed apex. 
Fig. 12 (after Treub). A portion of a longitudinal section through the pitcher 
of D. Rafflesiana, showing the inflexed apex in longitudinal sec- 
tion (ap.). 
Fig. 13. Mycelium on the inner surface of the wall of the outer pitcher of 
D. pectenoides. (xX 400. Slightly diagrammatic.) 
ap., morphological apex; d., depression at base of pitcher; g., median 
groove in wall of inner pitcher; /., lateral lobe of free margin of inner pitcher ; 
la., latex-cell ; m., free margin of inner pitcher; my., mycelium ; 2/., neck ; 
Pp, pointer inserted into the orifice leading into the cavity of the outer pitcher ; 
pet., petiole; pw., insect-puncture ; ro., rosette of hyphe. 
“Silver-Leaf’’ Disease. 
By Prof. Joun Percivat, M.A., F.L.S. 
{Read 5th June, 1902.) 
(PiatE 10.) 
THe disease known as “Silver-leaf” is, so far as I am aware, cou- 
fined to the Prune, and has been the subject of observation and 
investigation for more than a quarter of a century. The species 
which it most frequently attacks are the plum and peach, but it 
is not uncommon upon the apricot, and I have seen it occasionally 
upon the sloe. The leaves of the diseased trees are generally 
normal in form and size, but their surfaces, instead of being 
green, are of a peculiar ashy-grey colour, which is very readily 
recognized but not easily described. The affected trees produce 
little or no fruit, and although plants suffering from the disease 
may live many years before being killed outright, they are always 
sickly and unprofitable. 
A transverse section of the upper epidermis of @ healthy 
