44«*^ PRIMARY ARRANGEMENT OF TISSUES. 



Tagetes patula : neither the cotyledons nor the lateral portions of the lamina receive 

 fascicular passages in this plant. On the other hand there is on either side along tie 

 margin, in the parenchyma of the lower side of the leaf, an unbroken series of oil-con- 

 taining (schizogenetic) sacs, closed blindly on both sides (comp. p. 201). 



Finally, in the Cichoriacea^ the oil passages are wanting in all parts in most species 

 investigated, and in the stems and leaves of all species. But in the root of Scolymus 

 grandiflorus van Tieghem found them in groups of five, with exactly the same position, 

 origin, and structure as the primary ones of the roots of the Senecioneae. And in the 

 diarch main root of Cichorium Intybus and Lampsana communis there are also rudiments 

 of passages, there being the characteristic cell-divisions, but no opening of the passage 

 at those points of the endodermis where they arise in other Compositae. Scolymus is 

 therefore the one known member of the Cichoriacea: which really has oil passages in 

 addition to the laticiferous tubes. 



The case seems to be different with the relations between the occurrence of oil 

 passages and that of the sacs with milky contents, which accompany the vascular bundles 

 (comp. p. 149). At least van Tieghem found both organs side by side in the upper part 

 of the stem and leaves in Cirsium arvense and Lappa ; it is true that in the leaves the 

 passages soon stop, and the sacs become the more numerous. The same seems to be the 

 case in other species, e.g. according to Trecul's and van Tieghem's statements in 

 Cynara Scolymus ; but on this point further investigations are wanted. 



All investigated Vmbelliferae ' have without exception a very complex system of longi- 

 tudinal usually anastomosing sap-passages, the contents of which are ethereal oils with 

 resin or milky mixtures of these bodies with mucilage and solutions of gum. 



In the primary tissues of the root the passages lie exclusively at the periphery of the 

 vascular strand, directly within the endodermis. Their formation starts from a portion 

 of the one-layered ring of pericambium situated in each transverse section opposite the 

 angle of each vascular plate. The number of the cells of this portion is always even ; 

 e.g. 6, 10, 12 ; the radial wall, which separates the two central ones (it may be called the 

 middle wall), is opposite the outermost vessel of the plate, in the extension of its median 

 plane. On both sides of it lies an equal number (e.g. 3, 5 ... ) of passage-forming cells. 

 These are at first rectangular in transverse section, and somewhat radially elongated. 

 Each then divides into two cells by a wall, inserted at the middle of its outer wall, in- 

 clined at about 45° to the radial wall facing the elongation of the vascular plate, and 

 meeting this further out than its middle ; of these two cells one is large and irregularly 

 5-angled in transverse section, and one small and triangular. The triangular cells lie at 

 the outer limit of the pericambial layer, the 5-angled cells extend through its whole 

 thickness ; the middle radial wall of the portion of the ring is met by two, all the rest by 

 one of the inclined walls. At the angles between each triangular cell and its 5-angular 

 sister-cell an oil passage arises by splitting of the walls ; this passage is situated at the 

 middle radial wall, and is quadrangular, being limited externally by the two originally 

 triangular cells which remain small, internally by two 5-angled cells; at all other radial 

 walls, however, a triangular passage is formed, limited externally by one triangular, and 

 internally by two 5-angular cells. Opposite each vascular plate both of two- and of 

 many-rayed bundles there arises a curved series of passages, the number of which must 

 always be uneven : one central one and on either side of it the same number of lateral 

 ones. The absolute number varies in species and individual between five and thirteen 

 opposite each vascular plate. The middle quadrangular one of the passages of each group 

 is the largest, and the width of the rest diminishes as they are further removed from it. 



In addition to these passages, which correspond to the vascular plates, one smaller one 

 appears rather later in the middle of each sieve-group. It is pentagonal in transverse 



' Jochmann, De Umbelliferarum Structiira, Berlin, i!^54. — Tiecul, Comptes Rendus, lom. LXIII. 

 pp. 154, 201 C1866). — N.J. C. Miiller, in Pringsheim's Jahrb. V. I.e. — Van Tieghem, Ann. Sci. Nat. 

 5 ser. XVI. Compare above, § 50. 



