ARRANGEMENT OF THE LATICIFERQUS TUBES. 437 



(of resin ?), suspended in a fluid, whicll is almost always in the highest degree rich in 

 tannin ; in M. zebrina alone it is frequently destitute of tannin, according to Trecul. 

 After the action of alcohol or potassium bichromate, a very sharply defined coating of 

 the wall appears, resembling a contracted primordial utricle, and this likewise shows the 

 tannin reaction (investigated in M. Cavendishii). 



Besides that in the laticiferous tubes, tannin also occurs as a principal constituent of 

 the contents in single scattered, short, parenchymatous cells, and in isolated cambiform 

 cells in stem and petiole. 



The other Musaceae investigated have no laticiferous tubes, in spite of the fact that in 

 the rest of their structure they agree entirely with Musa. In place of them spaces usually 

 filled with tannin are found in cross-sections of Urania speciosa and Strelitzia, in the 

 neighbourhood of the thicker vascular bundles; these appear to be the laticiferous 

 tubes ; the longitudinal section, however, shows that they are only parenchymatous cells 

 or sacs with the contents indicated, which do not even form uninterrupted longitudinal 

 rows one with another. Those which succeed one another at different heights rather 

 belong, sometimes to one and the same, sometimes to various other rows of parenchyma. 

 In the rest of the parenchyma, and in the phloem portions of the vascular bundles, 

 scattered tannin-sacs occur, as in the equivalent parts of Musa. Heliconia speciosa 

 and H. Bihai, according to Trecul, never show cells or sacs filled with tannin, with the 

 exception of single scattered ones in the phloem of the vascular bundles. The. same 

 applies to H. pulverulenta Lindl. Finally in Ravenala madagascariensis, &c., Trecul could 

 not find tannin at all, only the wall of individual cells of the leaf-sheath showed an indi- 

 cation of blue colouring after the action of iron sulphate for twenty days. 



II. NON-ARTICULATED LATICIFEROUS TUBES. 



7. Euphorbiaeeas. Of this family a number of species of Euphorbia have been in- 

 vestigated with accuracy. In the shrubby, more or less succulent forms of hot countries, 

 as E. splendens, E. Caput Medusae, canariensis, rhipsaloides, &c., the stem shows a 

 relatively thin ring of vascular bundles, or of wood and bast, which encloses a bulky 

 succulent pith, and is surrounded by a layer of cortical parenchyma, which is also thick. 

 The stouter, thick-walled, main trunks of the laticiferous tubes run close to the outside of 

 the ring of bundles ; they are scattered in the cortical parenchyma, either singly or in small 

 groups. Their course is in general longitudinal, though not rectilinear, but unflulating 

 both in the radial and tangential direction. They give off numerous branches which are 

 further ramified through several degrees (cf. Fig. 84, p. 191). Those of the first degree 

 do not differ from the main trunks, their direction also is the same. The branches of 

 higher degrees become successively narrower and thinner- walled, those of the last degree 

 have blunt blind ends. The direction of the higher degrees of ramification is very 

 various ; sometimes their course, like that of the primary tubes, is longitudinal ; some- 

 times they penetrate in a curved and undulating course between the cells of the cortical 

 parenchyma, sometimes individual branches pass through the latter towards the surface,, 

 and reach the inner side of the epidermis, where they end blindly, either at once, or 

 after running for some distance below it. Other less numerous branches pass through 

 the medullary rays into the pith, in the peripheral region of which they divide into 

 numerous thick branches, each of which usually has an isolated longitudinal course. 

 We therefore find laticiferous tubes scattered in the parenchyma, on the medullary 

 side of the wood also. Reticulate anastomoses do not occur. Where an H-shaped 

 connection between two tubes is found, this depends merely upon the form and direction 

 of blindly ending branches. In those species which have developed leaves (E. splendens) 

 the laticiferous tubes enter them, at first following the vascular bundles, and then sending 

 out numerous branches from these, through the parenchyma, which run in the most 

 various directions, and at last end. blindly. 



