Iviii Sir William Jackson Hooker . 
Of the plant-houses existing in 1841 about ten were of 
considerable size, and of these two only, an Orangery and 
the architectural Conservatory near the entrance gates, are 
still (1902) standing. The Orangery was built by Sir W. 
Chambers in 176T for wintering orange trees. It is the first 
plant-house of any importance erected in the grounds, and 
had been latterly used as a conservatory for the reception of 
such trees as had overgrown the height of the New Holland 
House. It was so occupied till the completion of the 
Temperate House in the Arboretum in 1863, when its contents 
were transferred to the latter, and replaced by Museum objects, 
as will be more fully described under Museums. It was 
almost the only remaining house heated by flues under the 
floor, the dry air from which was very unfavourable to the 
plants, as was the want of light. 
The other permanent building was the architectural Con- 
servatory near the entrance gates. It is one of a pair erected 
in 1836, the other is at Buckingham Palace. It was heated 
on Perkin’s system of innumerable coils of pipes, the size of 
ordinary gas-pipes, charged with steam 1 from twelve furnaces 
in the vaults. It was used for the same purposes as was the 
Orangery, and its contents were similarly disposed of at the 
same time, when these were replaced by tropical plants, chiefly 
small palms, tree-ferns, and aroids, not a few of which are 
still flourishing. With regard to the other old houses, some 
were destroyed and better provided, others were improved 
and added to, and the majority had the old system of heating 
by hot air from flues passing under the floor replaced by that 
of hot-water pipes. In the case of six of these houses the 
flues from their furnaces were conducted into one shaft, 
thus contributing much to the cleanliness of their surround- 
ings. Two span-roofed houses were doubled, one for tropical, 
especially economic plants, the other for Australian and New 
Zealand ones. 
The building of the great Palm House was commenced in 
1844 from the designs of Decimus Burton, F.R.S., and the 
1 At a later period this system was replaced by one of hot- water pipes. 
