and the Pith M Vegetables, 9 



There are two remarkable circumstances, however, which, in con- 

 nection with this subject, I cannot overlook. In the development 

 of shoots, it cannot fail to be remarked that the elonga,tion is gene- 

 rally less at the base of the shoot than in the middle, and again be- 

 pomes less at the summit. Contrast this fact with the observation 

 made in the Library of Useful Knowledge,* that the pith variesf 

 " in diameter in the same tree, even when young, being smallest 

 at the base of the stem, longer in the middle, and smaller again at 

 the summit, and these variations are observable in the growth of 

 each future year." Again, Hedwig has observed, that '^ in the 

 peduncle of the Colchicum autumnale, the rings of the tubes are 

 closer when it begins to appear above ground, than at the time of 

 flowering."t 



. These observations demonstrate the existence of some intimate 

 connection betwixt the pith and spiral vessels, and the elongation 

 of the stem. 



in conclusion, permit me to submit the following summary of 

 the principal reasons which induce me to view the spiral vessels 

 and pith, as the organs by means of which this peculiar longitudi- 

 nal increase of the plant is effected. 



1*^, These organs are essential to the plant or bud, previous to 

 its undergoing this peculiar development, but cease to be neces- 

 sary so soon as the elongation is completed. 



2c?, During the progress of this development, the plant under- 

 goes no modification, which cannot be ascribed to the agency of 

 other organs, with the exception of its longitudinal growth or elon- 

 gation ; and for the promotion of this, the spiral vessels, by their 

 structure, appear to be peculiarly adapted. 



3c?, The spiral vessels can be traced in every part of the plant 

 which undergoes this peculiar development, and. they have hitherto 

 l)een traced in such parts only, and no where else. 



Ahbey-Housey Arbroath, Oct. 6. 1830. 



• Veg. Phys. p. 18. 



t Keith, B. iii. C. 3. Sec. 2. 



VOL. III. 



