346 M. Lestiboudois on the Vessels of the Latex, 



or empty, according to circumstances. Lastly, their walls lose 

 consistence by maceration ; they are then rendered extensible, 

 and may assume the appearance of a simple filament ; indeed it 

 is possible to mistake a streak of granule-bearing liquid, more 

 glutinous and resistant than the walls themselves, for a tube. 



These tubes, moreover, exhibit transitions to the nature of 

 fibres, so that we see intermediate forms in every variety between 

 fibres with thick and porous walls and nearly obliterated cavity and 

 those whose walls are of extreme tenuity. The fibres are firm and 

 porous in completely formed tissues, whilst their walls are less 

 and less thick in proportion as the tissues in which they occur 

 are more recent; hence in tissues most lately produced they 

 exhibit that conformation which has led to their being taken for 

 laticiferous vessels : in all these instances their extremities are 

 formed in the same manner. The fibres not only present trans- 

 itional phases in the degree of thickness of their walls, but also 

 in the quantity of granular matter contained in their interior : 

 this substance grows scarcer in proportion as the tubes advance 

 in age, and as their walls augment in thickness and their cavity 

 contracts; yet, however reduced the diameter of their cavity 

 may be, it is rare that a certain number of granules is not found 

 in it. 



When the cavity is very distinct, the granules are often seen 

 in abundance ; but when the tissues are incompletely formed, 

 their walls are not very evident, and the granules within are in 

 scanty proportion. 



These tubes are met with in the fibro-vascular bundles, and 

 are not distributed in the medulla or in the parenchyma of the 

 bark, as are the proper vessels. 



To further demonstrate that these granule-bearing tubes are 

 not identical with vasa propria, it may be noticed that they 

 occur as well in vegetables having coloured juices as in those 

 which have not. Thus, Asclepias Syriaca and other species of 

 this genus, Acer platandldes, &c., have fibrous bundles very 

 distinct from the proper vessels, though erroneously assumed 

 by Mirbel to be milk-vessels, and are perfectly like the ordinary 

 cortical fibres, and pass through all those phases just described, 

 presenting thick walls and punctiform cavities, or thin walls 

 and very apparent cavities, containing few or many granules. 

 This fibrous tissue, as we have stated, accompanies the spiral 

 bundles in the leaves. The tubes which compose it taper and 

 decrease in length as they follow the course of the nerves in their 

 divisions, and concur in forming the network of the leaves. 



Their walls having lost their thickness, they cannot be any 

 longer so easily distinguished in the exterior zone of the cortical 

 fibres of the stem. However, in certain plants, as the Ficus 



