274 THE JOURNAL OP INDIAN BOTANY. 



do not alternate with the veins. Sometimes adjacent palisade arcs 

 or girders are connected together by transverse strands of palisade 

 cells. In E. hirsutus there is an extensive tissue of thin-walled 

 parenchymatous cells towards the upper surface on either side of the 

 mid-rib ; this tissue seems to form an articulation tissue which adds 

 to the strength of the system of strands of the articulation tissue 

 below the furrows. 



Spongy tissue is not developed in any of the members and thus 

 the ventilating system is quite reduced. The articulation tissue forms 

 a characteristic feature of species of Gramineae ; it is composed of 

 thin-walled cells with a double function — that of collecting water and 

 that of assisting the halves of the leaf-blade to curve upwards. The 

 conical shape of the cells of the upper portion of the strands of the 

 articulation tissue is especially suited to this purpose. 



The veins are provided with bundle-sheaths of thick-walled 

 green cubical cells. The bundle-sheaths form complete rings round 

 non-transcurrent veins and arcs on the sides of vertically transcur- 

 rent veins excepting E. aristata in which all the vertically transcurrent 

 veins are provided with complete sheaths. The bundle-sheaths in 0. 

 Thomaeum and L. senegalensis are horse-shoe shaped and are incom- 

 plete on the lower side. As regards the function of bundle-sheaths, they 

 many form the means of inter-communication between the vessel and 

 the assimilatory tissue, as well as assist the latter in photosynthesis. 

 The veins are embedded in D. sanguinalis and in species of Panicum, 

 while they are vertically transcurrent above and below by stereome 

 bundles in D. bispinata, C. villosa, G. Boyleana. The veins are appo- 

 sed to the upper epidermis and are vertically transcurrent below by 

 stereome bundles in 0. Thomaeum. In E. interrupta the larger veins 

 are vertically transcurrent above and below by stereome bundles ; and 

 the smaller veins are apposed to the upper epidermis and are vertically 

 transcurrent below by stereome bundles. In other members the lar- 

 ger veins are vertically transcurrent above and below by stereome 

 bundles except in E. Boyleanus, C. catharticus and E. flagellifera, 

 where aqueous cells are found between the vascular bundles and 

 stereome bundles on one side or both sides ; the smaller bundles are 

 embedded. 



The veins either all lie in the same plane where the furrows on 

 both the surfaces are more or less equally deep, or they are placed in 

 two distinct planes where the furrows on the upper surface are deeper 

 than on the lower — the veins below the furrows being situated in the 

 lower plane. This arrangement of veins is well adapted to the curving 

 habit of the leaf-blade. 



