Natural History. 423 



pcriment, tends outwards. The experiment, therefore, has nothing 

 to do with the natural direction of roots and stems. 



Another theory considered is, that which views a tree or plant, 

 not as a simple individual, but as a union of universal independent 

 parts, arising each from a bud ; the bud being then considered 

 as a seed, which, under developement, produces latent roots that 

 descend, or tend to descend, towards the earth, and constitute the 

 fibres of the wood. In support of this theory, M. Poiteau quotes 

 the Rhizophora, growing on the borders of the Mahuri at Cayenne ; 

 the trunks of which produce roots at different heights, and are obli- 

 terated at the parts inferior to these roots, because, according to 

 M. Poiteau, the fibres of the lower buds no longer descend to the 

 bottom of the tree, but become and constitute these aerial roots. 

 The same is the case nearly with the Ludovia funiculifera, a plant 

 of Guiana, described by M. Poiteau. Many palms have their stipes 

 sustained by aerial roots, of which the most recent are the lowest : 

 to explain this fact, M. Poiteau remarks, that the growth of the plant 

 is from without inwards, from which he concludes that the youngest 

 woody fibres, being situated within, their prolongation should be 

 less than that of the more ancient fibres. — Bull. Univ. D. xiii. 74. 



2. On the Nature and Character of the Potato Root, and other 

 Vegetable Bidbs. — A particular investigation of the internal and 

 external organization of the Solanum tuberosum and Helianthus 

 tuberosus has been undertaken by M. Turpin, in consequence of 

 which he has been led to lay down the particular distinctive cha- 

 racters of the stems and roots of plants, and to class the two tubers 

 above mentioned with some others as true vegetable stems. 



The essential character of roots, in whatever medium the latter 

 may be developed, is the entire absence of vital nodes, or of those 

 points generally expanded and disposed symmetrically, and in deter- 

 minate situations on the surfaces of stems, and consequently of the 

 foliaceous appendages which always accompany buds. The multi- 

 plication of their fibres is always adventitious, has no determinate 

 regularity, and may take place from any part of their surface. 



The essential character of stems, whatever the medium in which 

 the latter are developed, is the occurrence of vital nodes, disposed 

 symmetrically, and constantly bordered, or accompanied by a fibra- 

 ceous appendage, which is sometimes reduced to its rudiments, 

 or, i/ideed, almost absorbed. Buds and bulbs grow from these 

 vital nodes, which are their true receptacles. 



A long and accurate series of observations are then gone into, by 

 which it is shewn, that the roots of the descending parts, and the 

 adventitious fibres of the potato, never do, under any circum- 

 stances, thicken, so as to produce a tubercle, such as could be 

 called a potato ; and that the same is the case with the Helianthus 

 tuberosus, or Topinambour. 



True stems, which arise from the lowermost vital nodes or buds 



