402 NATO RAL SCLANGE., JUNE, 
cases in which the leaves fall, showing either a complete brown or 
yellow discolouration, or only a partial one limited to the apex, margins, 
or base, or restricted to minute specks, or irregular patches scattered 
over the surface. Sometimes the leaf falls uninjured; according to 
Mr. Watson, during some recent fogs bushels of healthy-looking 
leaves were gathered up almost every morning in the Palm House at 
Kew. 
The local blotchings of the first class are presumably due to the 
action of an acid on the upper surface of the leaf. The layer of dirt 
deposited by the fog contains an appreciable amount of sulphuric acid, 
the product of oxidation of sulphurous acid. The frequent wetting of 
the leaves brings this into solution and the drops having a tendency 
to collect at the tips and margins will leave there on evaporation a 
deposit of acid. This process is continually repeated until sufficient 
acid accumulates to corrode the surface. 
The changes in the leaf which cause its rapid fall, with or with- 
out a colour change, are, the author thinks, largely due to an attack 
on its delicate unprotected internal tissues. The fog effects an entry 
through the stomates into the system of intercellular spaces, where 
its poisonous ingredients come in immediate contact with the moist, 
delicate, and unprotected membranes of the living cells, which offer 
but little resistance, and the protoplasm is directly attacked. 
Whether the leaf succumbs or not depends on the inherent consti- 
tution of the protoplasm. The process was carefully followed in leaves 
of Rhododendrons and others, and the action was found to begin in 
the lower layers of the spongy tissue next the stomates. Thence it 
spread to the upper parts of the leaf and the epidermis. In the case 
of thin uncuticularised leaves when the epidermis is very soft, the 
noxious vapours may enter directly through the outer layer, as well as 
by the intercellular spaces. It is not clear to what component ofthe 
fog this second class of injuries is due. Owing to the very general 
absence in the injured leaves of acid products of the green colouring 
matter, sulphurous acid cannot be the sole agent, and Professor 
Oliver thinks that some complex organic bases like pyridine may 
play an important part. As regards remedial measures, there seems 
but little to be done, except, as Lindley long ago suggested, to keep 
the temperature as low as is compatible with the life of the plant, 
with sufficient humidity to avoid desiccation. If the houses are 
otherwise tolerably air-tight, a contrivance for filtering the incoming air 
through boxes containing trays of charcoal sticks may be used to 
mitigate the evil. 
A TECHNICAL EDUCATION CONFERENCE. 
On April 20 and 21 the Senate House at Cambridge was the 
scene of a Conference on the relation of Universities to the County 
Councils in regard to technical education. 
