450 Proceedings of the Royal Irish Academy. 



wiiich gave rise to the first compound bundle. In this way, diametri- 

 cally opposite the midrib, there is to be found in transverse sections 

 of the base of the petiole, a single large bundle, fonned by the union 

 of four to six bundles of the leaf {cf. PI. xiy., figs. 26 to 29). The 

 bundles pass from the petiole to the stem in a manner before described. 



Approaching the apex of the leaf the bundles undergo frequent 

 fusions, but these seem to take place symmetrically on each. side. 

 Yery close to the extremity of the leaf there are but five. These 

 then fuse to form three, and these again unite into one. 



The parenchymatous tissues of the leaf of V. teres are not 

 differentiated from one another at all so sharply as is usual in flat 

 leaves. All the parenchyma within the epidermis, when viewed in 

 transverse section, appears composed almost solely of thin-walled cells, 

 with rounded outline, containing chlorophyll. There is no differenti- 

 ation into spongy and palissade parenchyma. This is of course what 

 we would naturally expect from the vertical position, and peculiar 

 shape of the leaves, in which the dorsiventral or bilateral symmetry 

 usual in horizontal leaves is modified into a more or less complete radial 

 symmetry. The cells of this parenchyma are oval when seen is trans- 

 verse section with the long diameter of the oval directed perpendicu- 

 larly to the curve passing through the inner larger bundles. The 

 outline of the cells included within the bundles is more irregular than 

 those lying outside. The parenchymatous cells of the leaf appear oval 

 in longitudinal section also, their longest axis lying longitudinally 

 in the leaf. Besides these rounded cells which form the great bulk 

 of the tissues of the lamina there are larger cells with thickened 

 walls containiag raphides and slime, which lie irregularly scattered 

 through the parenchyma. These cells do not contain chlorophyll. 

 Apart from this there is very little differentiation of the parenchyma- 

 tous tissues of the leaf ; the hypoderma is represented by a layer of 

 cells, somewhat smaller than the inner cells; a cortical bundle sheath 

 or phloeoterma is wanting in accordance with the rule observed by 

 Strasburger, that in those cases where a strong sclerenchymatous 

 sheath morphologically belonging to the vascular tissues accompanies 

 the bundles into the leaf, the radial walls of the cells of the innermost 

 layer of the cortex do not resist the action of H2S04, i.e. are not cuti- 

 cularized, as they do in those leaves where a typical phloeoterma is 

 developed : in other words the function of the endodermis is performed 

 by the vascular tissues, and no endodermis is developed from the 

 cortex. 



jMobius {loc. cit.) has ali'eady noticed the beautiful fonn of the 



