THE SECRETARY'S PORTFOLIO. 207 



ANNUAL ROOTS. 



At a late meeting of the Academy of Sciences, at Philadelphia, Mr. Thomas 

 Meehan notices some of the hypotheses relating to the eccentricity of the 

 annual wood layers. Mr. Meehan, in controverting the hypothesis that the 

 thickening was in consequence of the rootlets near; or in consequence of the 

 sloping of trees, thus causing a thickening on the under side, held the hypoth- 

 esis to be inconsistent, and thought the true cause of the thickening of woody 

 layers more on one side than the other, had yet to be explained. The rooting 

 on the under side could not cause the thickening of the wood, as Wistaria and 

 many others which he mentioned, rooting on the ground as they ran, did not 

 thicken in consequence ; while Ampelopsis did, as well as the poison vine. The 

 rootlets by which the poison vine attached itself to the trees, had been referred 

 to as being of some age ; but this was a mistake, as in most cases, save some 

 orchidere and a few other plants, aerial rootlets, like rootlets beneath the earth, 

 were mostly annual. The whole root system of plants was, indeed, but the 

 analogue of that system which existed in the atmosphere. Morphology had 

 made a great stride when it pronounced all the parts of the inflorescence but 

 modified leaves. Botanical science had yet to go further. The whole plant 

 was but a modified leaf, roots as well as branches. The same general laws that 

 we found in the aerial system, therefore, had their correspondence in the 

 terrestrial one. In the terrestrial system we generally saw a marked difference 

 in the leaves and branches ; but in some cases, as the arbor-vitae and deciduous 

 cypress, the two were so blended together, that at the annual "fall" season 

 branchlets and leaves all fell together. In these cases we saw that some of 

 these compounds of leaves and branches, — those the most favorably situated as 

 regards nutrition, — maintained a hold on life, and, once jiassing this critical 

 time, had an indefinite lease of life thereafter. It was precisely the same with 

 the rootlets of trees. They were the representatives of leaves, and myriads 

 died every year. Only here and there one endowed with greater vital privileges 

 escaped the annual "fall," and then it became a "root," with various terms 

 of endurance. Aerial roots, used by some creeping vines, were under the same 

 laws. Now and then one would find itself in the soft crevice of an old wall, or 

 in the decaying hollow of an old tree, and thus becoming a permanent feeder 

 to the vine. In England the evergreen ivy had been cut down near the ground, 

 after running for years over old ruins, and had continued to live on. But in 

 these exceptional cases it was found that some of the rootlets, as the rule, 

 annual, had found some soft place and taken on a permanent character, — 

 had become real feeding woody roots. He exhibited some old stems of 

 Ampclojjsis Virgiiiiana, which for years had been hanging unattached from 

 the branches of a tree, and which had eccentric wood, as in the attached poison 

 vines, and the surface was covered with aerial roots, which were produced and 

 died annually. 



