148 THE PRINCIPLES OF FLORICULTURE 



gases. We noticed there the importance of the part 

 played by the sun's rays in the preparation of plant food. 



The proper amount of light which plants of different 

 species should receive has never been demonstrated satis- 

 factorily. We know in a general way that the growth of 

 species, classed as " shade enduring," is often retarded by 

 being placed in strong sunlight. Again, the growth of 

 plants accustomed to strong sunlight becomes unhealthy 

 and weak when placed in the shade. Most flower crops, 

 however, demand maximum sunlight. Many foliage 

 plants, as palms and ferns, are injured by it. Light 

 conditions in greenhouses should be carefully studied. 

 Greenhouse management is intensive agriculture and the 

 amount of capital invested in structures and maintenance 

 is considerable. The returns should be the greatest 

 possible, which means that advantage should be taken 

 of every factor which increases the efficiency of the house. 



As has been observed, carbon assimilation is proportion- 

 ate to light intensity. Therefore, for most greenhouse 

 crops, an increase of light increases the ability of the plants 

 to assimilate food and to make a more rapid growth and 

 development. 



Among the things to be considered in improving the light 

 conditions of greenhouses, may be mentioned the follow- 

 ing: placing the houses so they will get the maximum 

 amount of light during the day ; giving such an angle to 

 the pitch of the roof as will allow the sun's rays to strike 

 the glass more nearly at right angles ; eliminating shadows 

 from eaves and overhead pipes ; using larger and better 

 glass ; laying glass so that there is a mimimum amount of 

 lapped area ; reducing the amount and size of the wooden 

 parts of the superstructure ; building larger houses and 

 eliminating partitions from the interiors. 



