106 PLANT-LIFE ON LAND [ch. 



Plainly as the years go on the result becomes rapidly 

 very large. Already Linnaeus had calculated that if 

 an annual plant produced only two seeds, and their 

 seedlings next year produced two, and so on, then in 

 twenty years there would be a million plants. This 

 is, however, a very slow rate of breeding, and it will 

 be well to enquire what are the rates of production 

 of germs seen in well-known plants. Taking first the 

 case of Seed-plants, the following table gives the 

 results of careful computation by Kerner of the 

 number of seeds produced in a single season by an 

 average specimen of each : 



Henbane {Hyoscyamiis niger) 10,000. 



Radish {Raphanns Ra^yhanistrum) 12,000. 



Plantain {Plantago major) 14,000. 

 Shepherd's Purse {Capsella Bursa-iyastoris) 64,000. 



Fleabane {Erigeroii Canadense) 120,000. 



Tobacco {Nicotiana Tabaemn) 360,000. 



Flixweed {Sisijmhrimn Sophia) 730,000. 



Extreme cases of productivity were found by 

 Darwin among the Orchidaceae, and his estimates of 

 the numbers of seeds were as follows : 



