438 



PRIMARY ARRANGEMENT OF TISSUES. 



The tubes are uninterruptedly continuous throughout the entire plant. No trace of 

 an articulation ever occurs (with exceptionof the formation of isolated cross-walls, 

 mentioned at p. 196). It has never been found possible to dissect out from a piece of a 

 stem, a tube of which even one of the main branches or trunks was closed blindly at 

 both ends. Trgcu! isolated a portion of a tube from the stem of E. globosa, the united 

 ramifications of which were together 93-5 ™™ in length, and had 120 points of branching; 

 yet 7 main branches and many smaller ones were torn off. I have isolated many main 

 branches from the stem of E. splendens up to 50-70™™ in length, without ever finding 

 a blind end to them (i. e. apart from the shorter lateral branches). In the growing-point 

 of the stem, branches, and roots, and in young rudimentary leaves, the laticiferous tubes 

 extend close up to the extreme apex, even before the development of the first elements 

 of the vascular bundle, and are always to be clearly recognised as branches which start 

 from the tubes in older parts, and penetrate into the meristem in course of formation. 

 Even in the seedling (investigated in the case of embryos of E. resinifera Berg.) the 

 laticiferous tubes behave as described above, with the sole difference that their ramifi- 

 cations are as yet less abundant than in the older plant. It follows from these facts, that 

 all the tubes of the plants in question are branches of a few primary ones, which, 

 originating in the embryo, grow on and on with the stock, and put out their branches 

 into the newly formed meristems and tissues. Cf. Chap. VI. 



The embryo and seedling of the native, herbaceous Euphorbiae (Tithymalus, Klotzsch 



and Garcke) show the same points of origin 

 of the tubes as the species discussed above, 

 while the mature plant shows the same con- 

 tinuity of all of them as branches of a few 

 primary trunks, which first appear in the 

 cotyledonary node (cf. p. 196). • In corre- 

 spondence with the entire growth and struc- 

 ture, the course of all their branches is different 

 from that in the succulent shrubby forms, 

 especially in the stem. In the intemodes of 

 E. Lathyris (cf. Fig. 190) the thicker main 

 branches of the tubes lie in the parenchyma 

 of the cortex, outside the fibrous strands which 

 support the phloem of the vascular bundles, 

 occurring isolated and in small numbers 

 between the parenchymatous cells. They 

 here have a fairly straight course through the 

 internode, and are little, if at all, branched. 

 In the node, on the other hand, abundant 

 ramifications, with a variously curved and in- 

 tertwined course, occur (Fig. 190), sending 

 out from here further branches, some of 

 which ascend, with the arrangement de- 

 scribed, into the cortex of the next higher 

 intemodes, some enter the leaves and axillary 

 buds, at first following the vascular bundles, 

 while others finally, in these regions, pass between the vascular bundles into the pith of 

 the stem, and then descend scattered singly between the parenchymatous cells of the per- 

 manently succulent peripheral portion. The inner part of the pith, which soon dries up, 

 contains no laticiferous tubes. Finally, numerous thin branches proceed from the node ; 

 these pass along the intemodes near the epidermis, and together form a hypodermal 

 system of tubes. They ascend vertically from the node into the internode next above, 

 and usually run between the first and second hypodermal layer of parenchyma, more 

 rarely directly below the epidermis, with a straight upward course and ramifying here and 



FIG. 190.— Euphorbia Lathyris; radial longitudinal section 

 through half the node and the neiglibouring portions of the inter- 

 nodes of a mature stem, together with the base of a leaf; 

 slightly magnified ; m pith, b portion of a bundle of the leaf- 

 trace, h secondary wood, I bast layer of the stem. The dark 

 lines marked r are the laticiferous tubes ; the short black lines 

 and points in the node are fragments of the web of laticiferous 

 tubes occurring there. From this two laticiferous tubes belonging 

 to the bast, and two hypodermal ones are seen passing upwards, 

 while four pass towards the pith; r hypodermal laticiferous 

 tubes. 



