406 M. Lestiboudois on the Vessels of the Latex, 



pias syriaca, Ficus elastica, Broussonetia papyrifera, and Cheli- 

 donium majus. 



In these plants, the reservoirs of the coloured juices clearly 

 constitute a vascular system such as one is accustomed to 

 conceive; there are tubes of more or less tenuity, frequently 

 isolated, though sometimes aggregated in bundles, which ana- 

 stomose and reunite to form larger trunks, are often flexuose, 

 with thin transparent walls, not lined by a lamina pierced by 

 fissures or pores, and without trace of a cellular organization. 

 They further contain a coloured fluid, varied in appearance by a 

 multitude of small granules held in suspension — these granules 

 being at times comparatively few, but at others so numerous as 

 to render the tubules altogether opake. After the granular 

 liquid is condensed by boiling, the granular matter is either 

 uniformly diffused through the tubes or agglomerated in irregular 

 masses. The tubules readily break across, and the disunited 

 fragments either remain in contact, giving rise to the semblance 

 of an articulation, or become detached and leave a thread of 

 the coagulated liquid they contained stretching between them 

 as an extensible connecting link. 



In leaves, these vasa propria are generally situated externally 

 to the bundles of cortical fibres and spiral vessels ; and they are 

 also met with alongside these bundles, either above or beneath 

 them, as, for example, in Ficus and Asclepias. 



Their arrangement may be readily examined in Asclepias, for 

 instance, by preparing the leaves in the following manner : — 

 After boiling them and leaving them to macerate for some days, 

 the epidermis is removed from the veins on the under surface, 

 and the transparent fibrous tissue situated beneath the spiral 

 vessels is then to be separated. On placing a small portion of 

 that tissue under the microscope, the vasa propria are readily 

 distinguishable in the form of opake wavy and branching ves- 

 sels, whilst the neighbouring fibrous tissue is seen to be formed 

 of transparent, very slender, straight, simple tubes with more 

 or less acute extremities, either empty or occupied with more or 

 fewer granules. 



The ramifications of the proper vessels are so disposed that 

 the several branches follow the plan of venation of the leaf; 

 some of them, however, are given off in advance of the venous 

 branches, and have rather the appearance of collateral vessels 

 than of ramifications of the vasa propria. Sometimes, again, 

 vessels which have been given off in company with a branch in 

 the system of venation send back a recurrent branch, which re- 

 traces its course towards the original point of departure of the 

 vessel — a fact, like the two former, also illustrated in the struc- 

 ture of the leaves of Asclepias. 



