C6 THE STRUCTURE OF FLOWERS. 



towards each otlier, as described in Hellebore, and are in part 

 required for the placentas. They are, therefore, no longer 

 oriented as in an axis, i.e. with all the vessels arranged on 

 the inner edge of the cord and facing the central medulla. 



A short distance above the base of the pistil, the inner- 

 most cords divide in a somewhat irregular maianer, but 

 rearrange themselves symmetrically round the centre of the 

 ground tissue in ten cords, as soon as the ovary cells have put 

 in an appearance. The method by which this condition is 

 arrived at was described by Yan Tieghem in Geranium 

 longipes, and with slight modifications it will apply to 

 Pelargonium zonale. Each of the lateral cords divides into 

 two (Fig. 13, 6), the two interior and adjacent branches 

 unite to form a single marginal cord with the tracheae 

 within or on the outer side (Fig. 13, c). The two outermost 

 branches pass oif to the right and left, and proceed to join 

 the corresponding halves from the neighbouring systems. 

 The pairs uniting thus form five cords of double origin, 

 alternating with the crescent-shaped marginal cords of the 

 carpels (r-). There are thus formed five in front of the ovary- 

 cells, and five in front of the septa , " which," Van Tieghem 

 observes, " one would regard as axial, if one did not pay 

 attention to the mode of formation of the coi^ds and to their 

 orientation." 



In his' description of Impatiens Boyleana, he says that 

 the two innermost branches (Fig. 13, &) unite at first end to 

 end, i.e. like an 8, with the tracheae at the extremities in 

 contact ; they then form one cord with the spiral vessels 

 towards the circumference of the section, by rotating through 

 90°, accompanied by complete fusion. 



In Pelargonium zonale, the tracheae become plunged, as it 

 were, within the phloem-tissue of the cords, as shown in 

 Fig 13, c, which then fuse together laterally. 



