CHAP. III. INJURING THE PRIMARY KADICLE. 187 



interval of 15 days, the part beneath the wire was 

 found to be very thin and easily broken, whilst the 

 part above was thickened. Now in these four cases, 

 one or more of the secondary radicles, arising from 

 the thickened part just above the wire, had grown 

 perpendicularly downwards. In the best case the 

 primary radicle (the part below the wire being 1J inch 

 in length) was somewhat distorted, and was not half 

 as long as three adjoining secondary radicles, which 

 had grown vertically, or almost vertically, downwards. 

 Some of these secondary radicles adhered together or 

 had become confluent. We learn from these four cases 

 that it is not necessary, in order that a secondary 

 radicle should assume the nature of a primary one, 

 that the latter should be actually amputated ; it is 

 sufficient that the flow of sap into it should be 

 checked, and consequently should be directed into the 

 adjoining secondary radicles ; for this seems to be 

 the most obvious result of the primary radicle being 

 pinched between the arms of a U-shaped wire. 



This change in the nature of secondary radicles is 

 clearly analogous, as Sachs has remarked, to that 

 which occurs with the shoots of trees, when the leading 

 one is destroyed and is afterwards replaced by one or 

 more of the lateral shoots ; for these now grow upright 

 instead of sub-horizontally. But in this latter case 

 the lateral shoots are rendered apogeotropic, whereas 

 with radicles the lateral ones are rendered geotropic. 

 We are naturally led to suspect that the same cause 

 acts with shoots as with roots, namely, an increased flow 

 of sap into the lateral ones. We made some trials with 

 Abies communis and pectinata, by pinching with wire 

 the leading and all the lateral shoots excepting one. 

 But we believe that they were too old when experi- 

 mented on ; and some were pinched too severely, and 



