10 



arranged in longitudinal rows ; and in the Acrogenic or scalariform, 

 which vessels are generally angular and present distinct facets, 

 the branches likewise come off in the same line, corresponding ge- 

 nerally to the angles of the vessel, but the spaces left between are 

 linear instead of round. Though these are the general characters, 

 intermediate ones are found which bring these three vessels in very 

 close relation to each other. 



The dots thus left in these several vessels, which appear so evident, 

 are not holes, as Mirbel, Richard and others have described, nor por- 

 tions of fibre broken up, as Bischoff mentions, but are spots on the 

 walls of the vessels where no deposit exists internally, corresponding 

 therefore to the meshes of the fibres, where the external membranous 

 tube of the vessel is unsupported ; and on account of the extreme te- 

 nuity of this tissue, and the minute space between the fibres, the light 

 in its transmission becomes decomposed, and every dot, under very 

 high magnifying power, appears of a greenish red tinge, and with a 

 low power as a dark spot. The structure of the dot is best seen by 

 examining the broken edges of any such vessels, when it will be found 

 that the fracture has been effected by the vessel giving way from one 

 dot to another, so that the torn edge of the membrane can be observed 

 in each dot. 



From these observations we become somewhat acquainted with the 

 minute processes Nature employs in forming fibrous deposits in the 

 interior of vessels, which may not however be very different from the 

 ordinary matter of bonification, yet it appears to me a mystery to un- 

 derstand what regulates this act of the plant. 



Schleiden, speaking of fibro-cellular tissue,* imagined " que par- 

 tout la spirale n'est qu'une modification de forme secondaire dans le 

 produit de la force vitale (la matiere des fibres), determine par une 

 autre direction de Taction vitale de la cellule, lorsque celle-ci, arrivee 

 a un certain degre de sa formation, est forcee d'abandonner son indi- 

 vidualite propre et d'entrer comme partie integrante dans l'etre com- 

 plexe qui constitue la plante entiere." Or in other words, to explain 

 this sentence, a cell at first possesses a perfect and independent exis- 

 tence, and forms its own membranous parietes ; but when perfectly 

 developed, it gives up its individuality when the vital power to form 

 secondary deposits, existing in the plant, occasions the fibrous depo- 

 sit. This reasoning, however, does not inform us what determines 

 the granules to take on definite arrangements. 



* Annales des Sciences Naturelles, xi. Botanique, p. 367. 



