and the Pith in Vegetables. 7 



the spiral vessels have not been fulfilled. Besides this, we know 

 that in the bud the pith and spiral vessels are essential to its fur- 

 ther development, because if they sustain any injury in the opera- 

 tion of budding it will prove fatal. Loudon directs the operator to 

 observe whether the eye or gem of the bud (which consists of the 

 pith and spiral vessels,) remains perfect; because if not, it is impro- 

 per, or, as gardeners express it, the bud has lost its root, and an- 

 other must be prepared. * 



It is evident, then, that the functions of the spiral vessels have 

 not been fulfilled in the bud ; and it has been already shown, that 

 in the full grown twig the spiral vessels are no longer necessary, 

 or, in other words, that their functions have ceased. Of course it 

 must follow, that it is during the progress of the development of 

 the bud into a shoot that the functions of these organs are in acti- 

 vity. Let us therefore compare the shoot with the bud, and en- 

 deavour to ascertain what modifications the former has undergone, 

 and what new organs have been formed in its development. 



On examining a young shoot after the first year's growth, it will 

 be found to consist of a pith, medullary sheath, ligneous layer, bark, 

 and cellular integument. In addition to the organs found in the 

 bud, therefore, we now have a ligneous and a cortical layer. But 

 neither of these have been generated through the agency of the 

 spiral vessels, for these are likewise produced on roots, where there 

 are no spiral vessels ; and we have already seen that ligneous and 

 cortical layers are produced in stems and branches where the pith 

 and spiral vessels have been wholly removed or decayed. What 

 other modifications, then, has the bud undergone in the develop- 

 ment of the twig ? Nothing but its longitudinal increase. It there- 

 fore remains to be inquired how far we are justified in ascribing 

 this to the agency of the spiral vessels. 



If the conclusions deduced from the facts before stated be cor- 

 rect, the functions of the spiral vessels were not developed in the 

 bud. Again, it is equally clear that their functions were developed 

 by the time that the growth of the twig was completed. During 

 this interval, the only modification which the bud had undergone, 

 and which could not "be ascribed to other organs, was in its longitu- 

 dinal growth : and as nature forms no organ in vain, and the spiral 

 vessels appear by their structure to be peculiarly adapted for facili- 

 tating the elongation of the stem, are not these sufficient reasons* to 

 justify the belief that the longitudinal increase of the twig is eflfect- 

 ed by means of the spiral vessels ? 



But if such be the case, it must foUow that spiral vessels must 

 be found in every part of the plant which may undergo a similar 

 development. Besides the stem, we know that the leaves, the 

 flower-stalk, the calyx, the stamens, the pistil, the cotyledons 



* Loudon Enc. of Gardening, 2057. 



