Vegetable Physiology/ for the Year 183^. 69 



distinguish them from ihe monocotyledons. He saw constantly 

 that the upper bundles between the vascular part and the 

 prosenchymatous part always force the others inward, and 

 thus isolate the one from the others. Each new fibre in tliis 

 manner occupies the place of one of the old ones, itself in turn 

 to undergo the same lot. Thus it happens that the prosen- 

 chymatous fibres, which are continually forced back to the 

 periphery, form the liber ; and the vascular fibres, which con- 

 stantly deposit themselves on the exterior of similar older ones, 

 form the wood ; this is the cause why he has named these two 

 parts of each bundle wood and liber, which alwa3^s remain in 

 the monocotyledons as they were first formed, undivided and 

 unchanged. 



Dutrochet's beautiful observations on the interior formation 

 of the ligneous bundle coincide entirely with Mohl's discovery. 

 He observed and figured in Clematis Vitalba this bipartition 

 of each bundle, which separating itself from its parts, leaves 

 the place clear for the one coming over it. And if he did 

 not notice which of the elementary parts it was which con- 

 stantly separated from the others, yet it did not escape hin), 

 that the change from the very beginning is divided into two 

 layers, which become organized at the same time, the interior 

 one into wood, the exterior one into liber. 



Although we cannot at first distinguish two separate zones 

 in the shoots of some species of Smilax, yet it has been de- 

 monstrated that the fibrous formations of the leaves occupy 

 the central point, and those of the bud the periphery; just as 

 Girou de Buzareingues found in the dicotyledons. But in 

 this the woody part alone helps to form those two systems, 

 while the part of the liber is forced back to the periphery ; in 

 Sinilax, however, and in other monocotyledons, the fibres re- 

 tain their perfect integrity. It must therefore be remarked, 

 that those for the most part peripherical proceed from pros- 

 enchymatous tissue alone, as Mirbel has figured it, and as 

 we can see it in diagonal sections on the side opposed to that 

 of the bud. 



The separation of the bundles which is mentioned by Du- 

 trochet, and described by Mohl, in the dicotyledons, answers 

 as a very convenient character for distinguishing the doubtful 

 cases. Thus for instance, in the stem of Piper, where some 

 vascular bundles remain in the parenchyma, even when a lig- 

 neous zone is organized near to the periphery, by which it is 

 inclosed, it is provided with medullary rays, and increases 

 annually by new layers. These bundles do not increase in 

 number; but if we examine them at difierent heights, we find 

 them in less number at the base and at the end, but in greater 



