44 
probably coloured with iron and not with copper. Prof. Norman 
Lockyer, C.B., F.R.S., —— e so good as to examine the light 
transmitted by ‘it. He reports :— 
* Cuts off red and blue onde of spectrum — ma 
“ Red-yellow reduced quite nine-tenths in inte 
* Blue reduced quite nine-tenths in intensity. 
* 'Tra vesci a fair proportion of orange, but most of light transmitted 
is yellow gree 
It “is pied that this is more severe than anything that was 
intended originally. But it is difficult, over a long period, without 
special precautions, to adhere to à standa rd. Mr. Robert Hunt (p. 383) 
stated that * the on iy abri sd which” his selected glass “ produces 
upon the rays of light is that it cuts off a smaller portion of the lowest 
red ray, and slightly diminishes the length of the yellow ray by increasing 
the green 
]t is va known that the effect of light of different degrees of 
refrangibility upon vegetation is by no means uniform, but has important 
peeuliarities characteristic of particular parts of the spectrum. This 
is too technical a od to enter upon here. But it is sufficient to say 
that the green glass in recent use at Kew, according to the modern 
data of Wageiaule physiology, gta about half the 
effective influence of ordinary sunlight on the processes of plant life. 
~ The general effect upon en as a —- is elearly exemplified 
by the recent experience of Zacharewiez (Annales A 
Dee. 25, 1894, pp. 589). He cultivated — under glass 
of different colours with the cem. ven results (p. 58 
Orange gave the maximum of veg E but at the e expense of the 
quality, : size, and earliness of the 
rdinary glass gave the finest add érlient fruits 
Violet gave the maximum production of fruit. but at the ‘expense of 
size, quality, and earliness 
Red, blue, and green were all injurious to the vegetative development of 
the plants, which became etiolat 
These results are, on the whole, in accordance with nA it is 
not, however, obvious why violet should be less injurious than gree 
Of late years at Kew the object aimed at in the use of green gia: shi 
been attained in great measure by the increasing haziness of Mis sky, 
due to the sinoke produced by the rapid extension of London to the 
south-west. Theextreme obseurity of the winter of 1883-6 showed that 
no available sunlight could possibly be spared. It became obvious that 
for the future the plant-houses must be so constructed as to exclude as 
little of the available sunlight as possible. The use of green glass was 
therefore abandoned in 1886 in all the houses except the fern-houses 
and the Palm-house. 
In 1889 the experiment was made of substituting white glass for 
n in the east wing of No. UL. (tropical fern-house). This was the 
result of the observation of the successful cultivation by Sir Trevor 
Lawrence, Bart., P.R.H.S., of ferns with full exposure to the light at 
Burford, near Dorking. The gr sn eas in the growth of the plants 
he mem soe 1892 a portion of the west wing was also reglazed 
n the same and the new + tenipeends fern-house (No. IIT.) was 
iro eme Sidi: white glass. The resuli with the Gleichenias and 
other half-hardy ferns was everything that could be desired. As the 
result of these these progressi ive experiments, it has now been determined to 
See eerie M reinigitioneitupat: ax Kew. 
