272 M. Lestiboudois on the Vessels of the Latex, 



moved from what we are accustomed to regard as that of vessels 

 properly so called. 



In the external layers of the bark the juices are contained in 

 cylindrical straight channels, simple or at times having some 

 anastomoses, which occupy the centre of the fibrous bundles of 

 the cortex. Their diameter is so considerable that they can be 

 detected by the naked eye ; and if their surface be scraped with 

 the edge of a sharp instrument, the fluid is seen to flow back 

 under the pressure. 



In the deeper layers of the bark, these channels of the proper 

 juices become smaller and smaller and more ramified, but they 

 occupy the same relative position ; that is to say, they occur in 

 the centre of the fibrous bundles. 



On the internal surface of the bark they assume the form of 

 a vascular network, with very slender ramifications and very 

 irregular anastomoses. 



These channels, however, notwithstanding their appearance, 

 are not true vessels. On examining under the microscope the 

 walls of such of them as occupy the centre of the bundle of 

 primitive cortical vessels, they are seen to be formed of short cells 

 (utricles) of a rectangular shape having thin walls, which appear 

 to be filled with the milky liquid. These channels consequently 

 are very analogous to the lacunse which enclose the resinous 

 secretions of the Coniferse, and to those of the Cycadese which 

 contain the gummy juices ; and there is no more reason for re- 

 garding them as vessels with cellular walls than for giving the 

 same appellation to the lacunae holding the gummy and resinous 

 secretions just referred to. The precise limit of their walls cannot 

 be assigned. The channels of the laticiferous juices of the 

 middle cortical layers have their walls similarly organized to 

 those of the external lacunae. 



With respect to the network of the inner cortical layers, it is 

 made up of cells apparently opake from the laticiferous fluid 

 they contain ; and no appreciable lacunae can be discovered be- 

 tween them. Their actual existence, however, cannot be denied; 

 for on cutting very thin sections of the tissue which contains 

 this network, and placing them under the microscope, the reti- 

 culations, naturally of an opake white, will be found to have 

 entirely vanished, as if the hquid to which the opacity is due 

 had escaped, and the cells which surrounded it had become 

 similar to the others in the tissue, and were no longer distin- 

 guishable from them. 



The root of the Sumach contains lactescent juices which 

 exude abundantly from the recently cut bark both of its larger 

 divisions and of its most minute i-amifications. On making a 

 transverse section of a large root, the white juices are observed 



