CHAPTER XII. 

 COURSE OF THE LATICIFEROUS TUBES. 



Sect, 131. The laticiferous tubes \ in most plants which are characterised by 

 their occurrence, traverse the entire body of the plant as a continuous system. 

 Exceptions to this rule seem, however, to occur; in the roots of Asclepias. 

 curassavica, and Cornuti, and of Periploca, I could not find them, but will not assert 

 their absence with complete certainty ; in the roots of Ficus elastica I only find them 

 in the secondary bast. 



As regards their relation to the other tissues, we may call them, as already indi- 

 cated above, companions, or in some places even representatives, of the sieve-tubes. 

 The latter relation is especially manifest in the secondary bast of many plants, to 

 which we shall have to return, below, Sect. 163. In the primary groups of tissue the 

 laticiferous tubes are distributed — 



(a) In the roots within the phloem of the vascular bundle. Only in the case of 

 the Euphorbise investigated do others occur in addition, which arise as branches 

 from those of the cotyledonary node, and lie close under the epidermis, separated 

 from the latter only by a few layers of cells (comp. p. 196)''. 



(i) In stems, petioles, and ribs of the leaves, the main courses or main trunks 

 of the tubes lie chiefly in the tissue surrounding the phloem-portions of the vascular 

 bundles, following the longitudinal course of the latter, and, as seen in cross-section, 

 scattered without strict regularity among the surrounding parenchyma. If the phloem 

 is sheathed by a strand of sclerenchyma they lie outside the latter. In addition to these 

 tubes, other smaller ones occur in certain cases, e. g. Cichoriaceae and Papaver, 

 which run in the phloem itself. In milky plants provided with phloem-portions 

 towards the pith, or with separate medullary bundles of sieve-tubes, these also are 

 accompanied by laticiferous tubes (comp. p. 338). 



In the foliar expansions, the tubes on the one hand still follow the higher orders 

 of ramification of the bundles ; on the other hand, in the majority of cases, they send 

 out branches which leave the paths of the vascular bundles, force their way in all 

 directions between the cells of the parenchyma, and end blindly, sometimes in the 

 inteiior of. the latter, sometimes at the inner surface of the epidermis. In the case 

 of Siphocampylus manettiseflorus, Tr^cul even states that the ends of the branches 

 pass between the cells of the epidermis, as far as its outer surface. In many milky 

 Dicotyledons, branches of the tubes also traverse the cortex of the stem, partly in the 

 internal parenchyma, partly hypodermally. In the succulent Euphorbias possessing 



' See Chapter VI, and the literature there cited. 

 ^ [Compare Scott, I.e., p. 143. (See p. 193).] 



