LATIFICEROUS AND VESICULAR VESSELS, ETC. 



Ill 



towards the primary cortex in scattered ramifications or recurrent knots, as also in 

 the pith if the stem is hollow. As in the last-named families, there is developed in 

 the horizontal partition-walls which the pith-tissue forms at the origin of each leaf-stalk 

 in the hollow of the stem, a rich reticulation of laticiferous vessels which penetrates 

 across the horizontal partition-wall in countless ramifications and in several layers one 

 over another, and connects the sacs of the medullary rays and of the whole wood- 

 cylinder. In the Papaveraceae (Cheli- 

 donium, Papaver, Sanguinaria) the lati- 

 ciferous vessels are also very perfectly 

 developed ; they are not here, however, 

 as in the families just named, united in 

 band-like groups, but they run mostly 

 at a greater distance from one another, 

 dispersed through the phloem and the 

 surrounding parenchyma ; single ones 

 appear also in the pith, but do not pene- 

 trate into the xylem ; lateral out- 

 growths and cross-anastomoses are found 

 seldom in the stem, but abundantly in 

 the leaves, and especially in the carpels 

 in which close-meshed reticulations are 

 formed in the parenchymatous funda- 

 mental tissue (Unger) ; similarly also in 

 the cortex of the root. In this family, 

 especially in the root- parenchyma of 

 Sanguinaria canadensis, the origin of the 

 laticiferous vessels from the coalescence 

 of cell-rows (absorption of the walls 

 between adjoining cells), may, accord- 

 ing to Hanstein, be proved ; imperfect 

 unions occur in this case, in conse- 

 quence of which the sacs appear bead- 

 shaped. The richly developed system of 

 the laticiferous vessels of the Urtica- 

 ceae, especially of Ficus and Humulus, 

 runs in the cortex in close proximity 

 to the fibro-vascular bundles of the bast, 

 in Ficus also in the pith, but not in the 

 wood; but they are neither so abundant 

 nor so evidently segmented as in the 

 Papaveraceae, nor so regularly combined 

 into a close-meshed net-work as in the 

 Cichoriaceas ; they rather run within 

 each segment of stem almost singly and 

 uninterruptedly as uniform tubes, only occasionally putting forth a branch or uniting with 

 another tube. In the nodes and leaves, on the other hand, they form numerous rami- 

 fications, sometimes united into a network ; or small, fine, obtuse prolongations, as in the 

 Cichoriacae. In the thicker leaves of many figs they are widely dispersed through the 

 parenchyma, and extend to close beneath the epidermis. The laticiferous vessels of Eu- 

 phorbiaceae are so far similar to these that they also belong to the branched description, 

 and are abundantly distributed through the parenchyma of the fundamental tissue ; but 

 they are distinguished by possessing thicker walls, and being similar, in transverse 

 section, to the bast-fibres. Developed most abundantly in the neighbourhood of the 

 bast-fibre-bundles, they sometimes entirely replace them {Euphorbia splendens) ; from 



Fig. 94. — A tangential transverse section through the phloem of 

 the root oi Scorzonera. hisfiamca ; a number of laticiferous vessels 

 anastomosing laterally among one another run through the paren- 

 chymatous tissue ; B a small piece of a laticiferous vessel with the 

 adjoining parenchyma-cells, more strongly magnified. 



