182 



in which the tubers are naturally deposited." " Many of the 

 joints of the plants during the experiment became enlarged and 

 turgid ; and I am much inclined to believe," he states, " that if I 

 had prevented the formation of regular tubers, these joints would 

 have acquired an organization capable of retaining life, and afford- 

 ing plants in the succeeding spring." So far as the writer has 

 been able to ascertain, this records the first successful attempt to 

 secure experimentally the formation of potato tubers in the light, 

 and is the first record that tubers can, under any circumstances, 

 form on the aerial portions of the shoot. 



On another variety of potato, as soon as tubers began to form 

 normally, Knight nearly detached many lateral aerial branches, 

 leaving them connected only by enough "alburnous and cortical 

 fibres and vessels as were sufficient to preserve life." After this 

 treatment small tubers formed in the light at the base of the 

 leaves of the depending branches. This experiment was one of 

 many, performed by the same keen observ^er and thinker, to prove 

 that sap may pass down in plants, and that the descending cur- 

 rent, though normally passing through the bark, as he had pre- 

 viously demonstrated,* may, under certain circumstances, travel 

 downward through the alburnum, or sap wood. 



Three years later f. Knight succeeded in producing experimen- 

 tally " a profusion of blossoms " from the buds of the potato tuber. 

 By destroying the above-ground branches he also induced the 

 under-ground stem parts to depart from their habit and grow up 

 into the air and light. From these experiments he was led to 

 the conclusion that the runners on which the potato tubers are 

 formed, " are very similar in organization to the stem of the plant, 

 and readily emit leaves and become converted into perfect stems, 

 in a few days, if the current of ascending sap be diverted into 

 them ; and the mode in which the tuber is formed above, and 

 beneath the soil, is precisely the same." 



It is fortunate for agriculture that some of Knight's later con- 

 clusions are not wholly correct, else planting would, indeed, be 



* Knight. Account of some experiments on the descent of sap in trees. Phil. 

 Trans. 93 : 277. 1803. 



t Knight. On the origin and formation of roots. Phil. Trans. 99: 169. 1809. 



