CIRCULATION OF THE SAP. 65 



are naturally deposited. After an ineffective struggle of a few 

 weeks, the plants became perfectly obedient to my wishes, 

 and formed their tubers precisely in the places I had assigned 

 them. Many of the joints of the plants during the experi- 

 ment became enlarged and turgid ; and I am much inclined 

 to believe, that if I had totally prevented the formation of 

 regular tubers, these joints would have acquired an organiza- 

 tion capable of retaining life, and of affording plants in the 

 succeeding spring. 



I had another variety of the potatoe, which grew with Another cxpe* 

 great luxuriance, and afforded many lateral branches ; and ""^'^"^• 

 just at that period, when I had ascertained the first com- 

 mencing formation of the tubers beneath the soil, I nearly 

 detached many of these lateral branches from the principal 

 stems, letting them remain suspended by such a portion only 

 of alburnous and cortical fibres and vessels as were sufficient 

 to preserve life. In this position I conceived that if their 

 leaves and stems contained any unemployed true sap, it couM 

 not readily find its way to the tuberous roots, its passage 

 being obstructed by the rupture of the vessels, and by gravi- 

 tation ; and I had soon the pleasure to see that, instead of re- 

 turning down the principal stem into the ground, it remained 

 and formed small tubers at the base of the leaves of the de- 

 pending branches. 



The preceding facts are, I think, sufficient to prove that the Hence the ta- 

 fluid, from which the tuberous root of the potatoe, when bcrs are form- 

 growiog beneaih the soil, derives its component matter, exists fcendinc^from 

 previously either in the stems or leaves ; and that it subse- the stems or 

 quently descends into the earth : and as the cortical vessels, J^^^^s, througU 

 during every period of the growth of the tuber, are filled with 

 the true sap of the plant, and as these vessels extend into the 

 runners, which carry nutriment to the tuber, and in other 

 instances evidently convey the true sap downwards, there 

 appears little reason to doubt that through these vessels the 

 tuber is naturally fed. 



To ascertain, therefore, whether the tubers would con- gpo^y^j, ^C jj^^ 

 tinue to be fed when the passage of the true sap down the tubers imped- 

 cortical vessels was interrupted, I removed a portion of bark ^^ J'-^^ ^"^"* 

 of the width of five lines, and extending round the stems of descending 

 several plants of the potatoe, close to the surface of the ^^P' 

 ground, soon after that period when the tubers were first 



Vol. XVI.— Jan. 1807.— No. 65, F 



