HORTICULTURE 



249 



winter, are supplied with fresh vegetables from regions 

 where there is no frost. Then, as spring opens, fruits and 

 vegetables are shipped from more temperate regions. Later 

 vegetables and fruits come from the sections nearer the 

 great cities. This gradual nearing of the supply fields 

 continues until the gardens near the cities can furnish 

 what is needed. Then these Northern gardens reverse 

 matters and ship 

 their products 

 South. 



The market gar- 

 deners around the 

 great Northern 

 cities, finding that 

 winter products 

 were coming from 

 the South and 

 from warmer 

 regions, began to 

 build hothouses 

 and by means of 

 steam and hot- 

 water pipes to make artificially warm climates in these 

 glass houses. Many acres of land in the colder sections 

 of the country are covered with heated glass houses, and 

 in them during the winter are produced fine crops of 

 tomatoes, lettuce, radishes, cauliflowers, egg plants, and 

 other vegetables. The great perfection which these vege- 

 tables attain in spite of their artificial culture, and their 

 freshness as compared to the products brought from great 

 distances have made winter gardening under glass a very 



FIG. 218. SETTING PLANTS IN A COLD FRAME 



