418 



PLANT-HOUSES. 



growing kinds may not overrun or mix 

 with their more diminutive neighbours. 

 Fig. 571. 



These tanks are so arranged in regard to 

 level, that they have a fall from the highest 



Fig. 572. 



to the lowest point of H inches in the 

 feet, so that a change of water takes 

 place, but so slowly as to be scarcely 

 perceptible, e e shows leaden pipes 

 leading water from the tanks to the 

 bog department b b, which can be 

 kept drier or moister by this means, 

 as may be deemed expedient. M. 

 Sckell has constructed his aquarium 

 of oak posts and planks, a precau- 

 tion rendered necessary to resist the 

 severe frost to which the climate of 

 Munich is liable. We have, how- 

 ever, substituted pavement sides and 

 bottoms for the tanks in our figure, 

 as suiting our climate, and being 

 more economical and durable. The 

 bottom is well puddled before the 

 pavement floor is laid upon it. The 

 sides are formed of pavement set 

 on edge, resting on the pavement 



100 



floor, and thoroughly jointed. At the ter- 

 mination at / a waste-pipe is placed 

 in the bottom of the tanks, and con- 

 nected with an underground drain, so that 

 the tanks may be dried when deemed 

 necessary. 



From the section it will be seen that all 

 these tanks are under the ground-level, a 

 plan adopted to render them stronger, and 

 more easily made water-tight. There is, 

 however, an objection to this plan — viz., 

 the plants are too far from the eye, parti- 

 cularly those of smaller growth, which do 

 not rise much above the surface of the 

 w^ater. This might be easily remedied by 

 forming the tanks upon the surface in- 

 stead of under it ; by this means the walks 

 would be 2 feet under the level of the 

 surface of the tanks and bogs, and the 

 plants brought into a better position to 

 be examined. In this case, the sides 

 would require to be made of pavement 3 

 inches thick, and securely jointed at their 

 edges, both for strength and for retaining 

 the water. The form also might be im- 

 proved by forming the tanks and bogs in 

 concentric octagons round the basin a as 

 a centre, leaving an open passage from 

 the outer circle to the basin at any point 

 of the circumference most convenient, as 

 shown by fig. 573. The centre basin 

 might be furnished with the tallest of all 

 aquatic plants, and the lower growing 

 ones kept in the outer circle. To protect 

 the whole from frost during winter, as 

 most of the plants would be down, the 

 Fig. 573. 



