STRUCTURE.] LATHILEA. 219 



"As each bud gives off thirty or forty bundles of vessels, 

 and these being superadded to those of the branch, such a 

 plexus arises at the contracted junction of the second year's 

 branch, and that of the third year, that their course can 

 no longer be followed. Each of the woody plates, however, 

 continues to receive accessions throughout the life of the plant, 

 those of the inner series containing as many layers as those 

 of the outer. It is hence evident that the bundles first 

 arranged in the branch of the second year, on entering that 

 of the third year, must present a very complicated arrange- 

 ment of tissues. The increase of the stems in diameter being, 

 however, effected throughout the length of the plant by an 

 addition of matter to the outside of both concentric series of 

 wedges, it follows that the growth is in one sense at the same 

 time Exogenous and Endogenous. 



"However complicated the nature and disposition of these 

 tissues may cause the development of the stems to appear, 

 the order in which each wedge of wood and its layers of 

 pleurenchyma are deposited in the first year is the same in 

 Viscum ; nor are the tissues themselves very different from 

 those of that plant. " (Flora Antarctica, i. 298, with numerous 

 well-executed figures of the anatomy.) 



Among herbaceous stems that of Lathrsea, which has been 

 carefully studied by M. Duchartre, may be taken as a good 

 example of anomalous organisation. In the stem of this plant 

 he finds, as in all the stems of Dicotyledons, the pith, the 

 ligneous system and the cortical system formed of the liber 

 and of the cellular envelope ; but he noticed two characters 

 which appear to remove this plant from the usual structure 

 of these vegetables. The first consists in the absence of a 

 medullary sheath, that is to say, of a first interior zone of 

 vessels of a different nature to those of the ligneous zone, 

 and comprised between the pith and this ligneous zone. It 

 is these vessels which, in the ordinary Dicotyledons, belong 

 to the form designated by the name of true spiral vessels or 

 of unreliable spiral vessels, and it is in this position alone 

 that these vessels are found in the stem. Here nothing 

 similar occurs; the vessels nearest to the pith consist of 

 finely reticulated vessels, similar, although finer, to those 



