18 THE PLANT. 



itself become enlarged, and exert their influence in pro- 

 portion as the external conditions are ftivourable. 



The developement of the biennial plants cultivated for 

 their roots has three distinct periods ; in the first period 

 the leaves principally are formed ; in the second, the 

 roots, in which are stored the substances needed to pro- 

 duce the flower and fruit during the third period. 



A series of experiments, made by Anderson, upon 

 turnips, affords a clear view of the several directions in 

 which the energy of a biennial plant tends at different 

 periods of its growth. (' Journal of Agriculture and 

 Transactions of the Highland Society,' No. 68, 69, new 

 series, 5.) 



These experiments were made to ascertain the total 

 produce of vegetable substances obtained from turnips on 

 one acre of ground. The turnips were gathered at four 

 different stages of growth ; the first on July 7, the 

 second, on August 11, the third, on September 1, and 

 the fourth, on October 5. The following table shows the 

 weight of leaves and roots in pounds, taken up at the end 

 of the respective stages, and calculated upon one acre of 

 ground. 



The relative quantities of leaves and roots show that in 

 the first half of the time of vegetation, sixty-seven days, 

 the organic labour in the turnip plant is principally 

 directed to the production and developement of the ex- 

 ternal organs. 



From the 7th July to the 11th August, a period of 

 thirty-five days, we find the increase to be 12,574 pounds 



