LATICIFEROUS TUBES. 187 



-found in the CichoracecB, Campanulacece, Loheliacea (and, according to Tr^cul, in Gun- 

 delia Tournefortii, one of the CynaracecB), the Papayacecs, many Papaveracece (Papaver 

 Roemeria, Argemone, Chelidonium, but not Glaucium, Macleya, Sanguinaria), many 

 AroidecE, and Musacem, The non-ariiculated tubes are found in the Euphorbiacea, 

 UfticacecE in the wider sense (including the Artocarpeae, and Morese), ApocynacecB, 

 and AsclepiadacecB. 



The properties common to all are, firstly, that they traverse the whole length of 

 the mature parts of the plants as continuous, and, with rare exceptions (Musa, Che- 

 lidoniurri), frequently-branched tubes ; and not only do they traverse each single 

 member of the plant on its own account, but they send branches from these into all 

 the like and unlike lateral appendages. 



Secondly, all laticiferous tubes have, as was above noted, soft, apparently very 

 watery, smooth or flatly pitted cellulose walls, which often show the characteristic 

 iodine reaction of collenchymatous walls (cf. p. 120). These are in many cases 

 very delicate, and without recognisable minute structure : thus, e. g. almost universally 

 in the Aroideae, in Vinca, Asclepias curassavica, and in other cases in the thin 

 branches of higher order. The membrane of the stronger stems and branches of 

 most tubes is thickened, and appears as though swollen in transverse sections, having 

 delicate stratification, while striation is also seen, especially in the strongly-thickened 

 tubes of woody stems (species of Euphorbia, Nerium). The thickening increases 

 with age. Even in the very thick membranes no sculpture of the surface can be 

 recognised : on the other hand delicate transversely-oval pits are Often seen, e. g. in 

 the tubes of Plumiera alba, in those of the base of the stem of Campanula Medium 

 (Trdcul), and in old stems of Lobelia syphilitica. In the base of the stem of species 

 of Argemone are found crowded together band- and knot-shaped thickenings which 

 protrude inwards. The wall of the tubes of Plumiera alba may be split, according 

 to Trdcul, into spiral bands of 1 0/^-15 /* in breadth. 



Further, pits occur less commonly on the lateral walls than appears at first sight, 

 especially in articulated laticiferous tubes, since the lateral wall of these, especially 

 when old, has often very numerous and short protrusions, which give, in surface-view, 

 the figure of pits with delicate contour. I could never find support for those state- 

 ments, according to which the pits of the lateral wall have the structure of sieve- 

 plates. 



As will be more completely described in Chapter XII, but must here be only 

 briefly stated, the laticiferous tubes permeate the whole body of the plant, in most cases 

 as a continuous system, sending branches from the stem into all lateral members. 

 These branches often push their way between the elements of all regions, and of all 

 tissues of other sorts than themselves. As regards the main branches or stems of the 

 tubes however it is generally the case that they follow the vascular bundles, i. e. the 

 wood and bast, as concomitants of, or sometimes even substitutes for the sieve-tubes. 

 In this course they often approach very closely in point of distance to Tracheae, 

 especially vessels, and on this circumstance, together with the above-mentioned 

 (p. 169) occurrence of apparently coagulated latex within the vessels of laticiferous 

 plants, depend the controversies on the anatomical relations between these two 

 series of organs. The fact is that the tracheae of the furthest ends of vascular 

 bundles in the laminse of leaves are often accompanied by branches of laticiferous 



