702 THE BOOK OF GARDENING. 



at the top of the roof, and also at the sides between the roof 

 and the ground. When the nights are cool, but the sun is strong 

 and bright during the day, the temperature may be kept up by 

 closing the ventilators early and storing the sun heat. 



In the frames air can be given by means of wooden blocks 

 notched in stair fashion, so that the lights can be raised 

 to various heights when it is not desired to remove them 

 altogether. 



Water Tanks. — Every house should be provided with w^ater- 

 tanks. These can be let in the ground on a level with the 

 floor, and service water laid on. But they should also be made 

 to collect all the rain-water from the roof, and this should be 

 used in preference to any other. It is as well to have a couple 

 of hot-water pipes running through the tanks, so that the water 

 may be heat^ed to the same temperature as that of the house. 

 Self-registering thermometers should be placed in every house, so 

 that variations of temperature may be observed. 



Cultivation. — After describing the structures for growing the 

 plants in it will be advisable to give a general outline of their 

 cultivation, proceeding to fuller details later on. 



As greenhouse plants vary so much in their habit and growth, 

 they require different methods of treatment and different com- 

 posts for growing in, the various soils for making which should 

 always be stacked for some time before using. 



Watering requires extreme care. It is almost impossible to 

 tell anyone how to water properly, but the cultivator who takes 

 a real interest in his plants will soon get to know the requirements 

 of each individual, and will water it accordingly. On no account 

 should a plant — except in special cases — be allowed to become 

 dry. V ery often a plant will suffer so much damage from being 

 dry for only one day that it will not recover during the rest of 

 the year. Generally if the pot in which a plant is growing gives 

 a hollow ring when tapped it may be said to be dry, but this 

 is not always a true test, and one can only tell correctly after 

 long experience. Again, care must be exercised not to over- 

 water, as quite as much damage can be done in that way. The 

 great art is to give a plant water just sufficient at the time when 

 it is beginning to require it. 



All plants w^hen potted should have perfectly clean pots and 

 good drainage. If this latter becomes blocked it must be 

 renewed, otherwise the soil will become sour and the plant w^iil 

 suffer. To prevent this, the drainage should be covered with 

 some loose material, such as dry leaves or moss. 



Worms are sometimes a great trouble in this respect. They 

 can often be got at by carefully knocking the plant out of the 

 pot, taking care not to injure the roots or break the ball. If this 

 cannot be done, watering with soot or clear lime-w^ater will 

 kill them. 



