28 



3. Flowering plants blossomed sooner and remained longer 

 in bloom. 



The writer found that in the case of ripening strawberries after 

 the fruit was swelled the incandescent light had good results. 

 Plants placed about 18 inches below the small lamps ripened 

 several days earlier than those beyond their influence ; the fruit 

 was sweeter and of a much deeper colour. 



In the year 1844 Dr. Draper, of the University, New York, 

 made some exceedingly interesting experiments to determine the 

 individual effect of the different coloured rays from the solar 

 spectrum upon plant growth. By means of a specially arranged 

 prism he separated the seven different colours, red, orange, yellow, 

 green, blue, indigo and violet, and arranged a box with seven 

 different compartments in which seeds had been germinated in 

 the dark, so that each compartment should have a separate colour 

 falling on it. Before long he noticed that those small plants 

 exposed to the yellow and adjacent rays turned green, but those 

 exposed to the extreme red and extreme violet underwent no 

 change. Sir William Siemens repeated this experiment with the 

 arc lamp, the different rays from which he caused to fall by means 

 of a special arrangement on mustard and cress grown in the dark. 

 The results he obtained confirmed Dr. Draper's theory. 



The arc lamp is very rich in red and violet rays, and in both 

 Sir William Siemens and Mr. Thwaite's experiments the naked 

 light had an injurious effect on the plants ; by screening off some 

 of the red and violet rays a great acceleration of growth was found 

 as compared with ordinary daylight. For these and other reasons 

 the mercury vapour lamp has many advantages over the arc lamp 

 for cultural purposes. It requires practically no attention ; 

 there are apparently no harmful rays from it, for though rich in 

 violet rays, results show that the glass tube and four or five feet 

 of atmosphere must cut off any injurious portion, and the 

 amount that reaches the plant has only a beneficial effect. In 

 the arc lamp the carbons require to be renewed about every eight 

 hours, and cost is. to renew, whereas the mercury lasts for 2,000 

 hours, which means two winter seasons, before it is exhausted, 

 when the tube can be renewed at the cost of about 2 is. The 

 initial cost of the lamp of the automatic type is about the same as 

 the arc lamp and the consumption of current is considerably less. 



A considerable economy is effected in coals for heating. A 

 single row of flow and return 5-inch piping is sufficient to keep up 

 a maximum temperature of 55 which seems to meet the require- 

 ments of certain plants better than forcing heat of 65 to 75. 

 They have not the attenuated and delicate appearance so often 

 seen in plants raised in heat and the saving of both labour and 

 space is an item of no small importance to the market gardener 

 which he would gain in being able to plant his seedlings in the 

 open air without any hardening off process being necessary. 



