366 INDEX. 



Beautiful adaptation of the atmosphere to plants and animals. Effect of 

 pure oxygen. Property of watery vapor in vegetable economy. Subtlety of 

 the air. Necessity of maintaining an adequate supply of aqueous vapor in the 

 atmosphere. Instruments for guiding us m regulating the atmosphere. In- 

 struments much wanted for measuring the respective quantities of the gaseous 

 elements, 305 



SECTION VI. 



PROTECTION OF PLANT-HOUSES DURING COLD 

 NIGHTS. 



Advantages of protecting bodies. Conditions of the plants at low temper- 

 atures. Light coverings otherwise useful. Experiments on the cooling 

 effects of wind. Materials for protecting glazed structures. Methods of 

 protection, 309 



Slight covering that is required to protect plants from frost. Experiments 

 of Dr. Wells on coverings. Method of covering. Distance to keep the cov- 

 ering from the object protected, ... 313 



Effects of vertical coverings. Horizontal coverings. Coverings of straw, 

 etc. Protection afforded by walls. Protection of snow. Warmth afforded 

 by the soil to trees in winter, 31T 



SECTION VII. 



GENERAL REMARKS ON THE MANAGEMENT OF 

 THE ATMOSPHERE OF HOT-HOUSES. 



Adjustment of the artificial to the natural atmosphere. Observations of 

 Knight. Rest necessary to plants during night. Cause of the imperfect 

 maturation of fruit-tree blossoms. High night temperatures exhaust the ex- 

 citability of the trees. Plants continue longer in bloom in low night temper- 

 atures. Admission of external air during day. Difference of climate be- 

 tween this country and England, 320 



Rules to be observed by the gardener in charge of hot-houses. Dutch meth- 

 od of forcing. Excessive moisture its effects. Necessity for periods of 

 rest to plants. Changing the period of fructification, 325 



SECTION VIII. 

 VENTILATION WITH FANS. 



Construction of ventilating fans. Methods of using them. Their adapta- 

 tion to horticultural purposes. Different kinds of fans. Objects to be ef- 

 fected by them. Requisites to the use of fans. Windmill ventilators. 

 Their employment in horticultural buildings. Pump ventilators. Ventila- 

 tion by means of chimney shafts, &c 329 



