62 THE JOUKNAL OF INDIAN BOTANY. 



with verrucose walls. Pericycle of groups of stone-cells. Pith of 

 thin-walled cells. 



Heliotropium paniculatura L— Figs. 215, 216. Woody. Meso- 

 phyll formed of palisade tissue on the upper side and of arm-palisade 

 tissue on the lower. Middle tissue present. Hairs unicellular and 

 with verrucose walls. A layer of colourless tabular cells on the inner 

 side of the assimilatory tissue in the axis. Endodermis with granular 

 contents. Pericycle formed of groups of stone-cells. Pith of thin- 

 walled cells with granular contents. 



Tricodesma indicum Br. — Figs. 217, 218. Quite herbaceous. 

 Mesopbyll formed of palisade tissue on the upper side and of arm- 

 palisade tissue on the lower. Veins with bundle-sbeaths. Middle 

 tissue absent. Sclerenchymatous pericycle not developed. Pith of 

 thin-walled cells. 



Sericostoma pauciflorura Sths. — Figs. 219, 220. Woody. 

 Mesophyll isobilateral. Middle tissue present. Hairs unicellular and 

 with verrucose walls. Pericycle forming a composite ring of stone- 

 cells. A layer of colourless tabular cells on the inner side of the 

 assimilatory tissue in the axis. Pith of thin-walled cells. 



Arnebia hispidissima DC. — Figs. 221, 222, 223. Herbaceous. 

 Mesophyll formed of palisade tissue on the upper side and of arm- 

 palisade tissue on the lower. Middle tissue absent. Veins with bundle- 

 sheaths. Hairs unicellular and with verrucose walls. Pericycle 

 formed of isolated stone-cells. Pith of cells with lignified walls. 



Structure of the Leaf. — The epidermal cells have the outer walls 

 greatly thickened. The inner walls are thin and more or less undu- 

 lated. The outer walls are muriculate in E. aspcra and A. hispidis- 

 sima ; they are convexly arched outwards inT. indicum and S. puvci- 

 florum. Some of the epidermal cells in H, rariflorum and T. indicum 

 are vertically elongated, while the rest are tabular or polygonal ; this 

 peculiarity in shape may be supposed to mark the commencement of 

 unicellular hairs (fig. 206.) These hairs have been observed at differ- 

 ent stages of development (fig. 206, 207, 208). It seems that the 

 epidermal cells at these spots divide by vertical walls ; the daughter 

 cells then elongate and present a shape as in (figs. 210, 217). One of 

 these daughter cells then elongates still more and gives rise to a small 

 unicellular hair with a large lumen and with a broad base. These 

 hairs will be discussed in greater detail under the hairy covering. 

 The stomata are usually placed in depressions produced either by 

 the thickened or papillose outer epidermal cells. The guard-cells 

 are in the plane of the surrounding cells. The stomata are more 

 numerous in members with a larger number of veins. In H. panicula- 

 t,um there is a sort of depression produced by the downwardly pro- 



