_^24 PRIMARY ARRANGEMENT OF TISSUES. 



blindly, either terminate together wHh the last vessels in the parenchyma of the leaf, 

 or similar terminal branches are sent out as far as the epidermis. 



For the course of the tubes in the peduncle and receptacle, essentially the same rules 

 hold good as for the stem : some branches of them accompany the small vascular bundles 

 which traverse the pistil, corolla, and stamens (Hanstein). 



In the roots the tubes lie in the phloem-groups of the original vascular bundles, and 

 thus within the pericambial zone— at least in Tragopogon and Scorzonera hispanica. 



They never enter the xylem groups unless it be in the ultimate ramifications of the 

 bundles, where they are in close contact with the tracheides, and in the nodal anasto- 

 moses, which pass through the medullary rays, between the medullary and the peripheral 

 bundles, where they may come to lie close to the vessels. 



2. The nets of laticiferous tubes of the Campanulaceas and Iiobeliaces are in 

 general quite similar in form to those of the Cichoriaceae. In their distribution a differ- 

 ence is in so far observable, that the chief seat of their occurrence is the internal phloem- 

 region, which lies towards the xylem-portions of the bundles. In the periphery of the 

 phloem and the parenchyma of the external cortex they are in many cases entirely 

 absent, or very isolated (Lobelia inflata, syphilitica, urens, Adenophora Lamarckii, Phy- 

 teuma Halleri, spicata. Campanula sibirica, medium, ranunculoides, grandis, lamiifolia) ; 

 more rarely they are abundant (Tupa salicifolia, Isotpma, Centropogon, Piddingtonia 

 spec), and especially in Tupa Feuillei, Ghiesebrechtii, and Musschia aurea, where they 

 penetrate up to the epidermis. In the case of Siphocampylus manettiseflorus, Trecul 

 states that individual ends of branches penetrate as far as the surface of the epidermis, 

 and even project there as small papillae. 



In those Campanulaceae which have sieve-tubes on the inner side of the woody ring, or 

 in the medullary bundles, the phenomena above mentioned are complicated by the occur- 

 rence of laticiferous tubes accompanying the latter, as in the case of the Cichoriaceae with 

 similar structure. They are absent in the xylem, in the secondary ring of wood, and 

 in the parenchyma of the pith in all Campanulaceae investigated, and in many Lobeliace^. 

 In other plants of the latter family on the other hand, e. g. Centropogon surinamensis, 

 Tupa salicifolia, Ghiesebrechtii, Feuillei, Siphocampylus manettiaeflorus, microstoma, and 

 Lobelia laxiflora, Trecul found them scattered at the periphery, and more or less deep 

 in the interior of the pith, and found that these medullary tubes are in communication 

 with the cortical ones by means of branches traversing the woody ring. 



3. The laticiferous tubes of the Fapayacese, investigated in Papaya vulgaris, Vascon- 

 cellea monoica, cauliflora, and microcarpa, form in the stem of these plants an abundantly 

 ramified and anastomosing net-work of tubes, extending both through the highly paren- 

 chymatous primary and secondary wood, and also through the medullary rays and the 

 bast-region. The main trunks have an approximately vertical course and form interrupted 

 rows approximately concentric with the circumference of the stem; the separate portions 

 of these rows everywhere alternate variously in wood and bast, with parenchyma, vessels, 

 and sieve-tubes. The neighbouring tubes are connected laterally with each other by 

 means of exceedingly numerous wide anastomoses. Similar anastomoses occur in the 

 most various particular forms, between the different groups and rows, both in radial 

 and tangential direction, the radial connections being often effected by long transverse 

 branches with an approximately horizontal course. Blindly ending branches and branch- 

 lets further occur with varying frequency. The tubes are usually separated from the 

 vessels by at least one layer of pairenchyma, some however are in contact with them, and 

 as discussed above (Chap. VI) there is perhaps open communication between the two. 

 Into the pith of the internodes, which soon disappears, the tubes do not enter ; they 

 form, however, a complex network, anastomosing on all sides in the medullary disk, 

 which is persistent in the nodes. In the primary cortical parenchyma, Dippel alone 

 found isolated tubes, accompanied as a rule by parenchymatous cells containing crystals 

 near the outside of the bundle of bast-fibres, and connected with the internal tubes by 

 very elongated horizontal transverse branches. 



