306 No)i-Isolablc Races. 



Sand-bed, 1 meter deep 



2 



Garden-soil 



On the control bed the distances between the plants 

 were somewhat greater, but as practically they did not 

 touch one another on the sand bed this fact does not 

 signify. 



The seeds employed in this experiment gave a larger 

 proportion of annual specimens than did those of the 

 previous one. Tlie main result is that the proportion 

 of plants which produce stems in their hrst year can Ije 

 reduced to about one-half by cultivation in a bed with 

 half a meter of sand, and to less than a quarter by culti- 

 vating in a meter of sand. 



The results of the foregoing experiments prove that 

 biennial species which possess, in a semi-latent state, the 

 capacity to produce annual specimens, can be induced to 

 manifest this anomaly to a much greater extent by sup- 

 plying them with more food. Crowding of plants, sha- 

 ding, lack of manure, or cultivation on sand, favor tlie 

 production of biennials ; but the more space, light and 

 nourishment in the soil there is at the disposal of the 

 individual plants the greater will be the number of those 

 which will produce stems, flower and ripen their seed 

 in their first summer. The stimulus of the winter or 

 spring frosts, which in other cases induces the young 

 plants to develop stems, is without effect here ; for under 

 the described conditions even seeds sown in the middle 

 of May in the open ground may give rise almost exclu- 

 sively to annual plants. 



Continued selection, however, fails either to fix the 

 biennial races and to free them of annual specimens, or 

 to free the annual races of biennial individuals. 



