94 INDIAN FOREST MEMOIRS. 



motor-cells by some writers 1 and bulli form-cells by others. 2 Beneath these motor-cells, and 

 therefore alternating with the principal longitudinal nerves, are smaller nerves, also 

 provided with girders and chlorenchyma rings, similar to those of the principal nerves, but 

 smaller. Immediately above the midrib is a thick, cushion-like, band of thin-walled colour- 

 less cells which is believed to function mainly as water-storing tissue. It is to be noticed 

 that this tissue is protected by a layer of sclerenchyma, one to two cells thick, which lies 

 immediately beneath the upper epidermis, while the bands of motor-cells are provided with 

 no such protection. 



When the leaf dries, the blade becomes convolutely folded inwards towards the upper 

 surface. There seems little doubt that this folding is effected mainly by the shrinking of 

 the motor cells and in a section which has been allowed to dry and fold under the micro- 

 scope, the leaf tissue on each side of a band of motor cells can be distinctly seen to have been 

 pulled inwards towards the motor cells. This convolute folding of the blade obviously re- 

 sults in the protection of the numerous stomata on the upper surface of the leaf and must 

 therefore considerably reduce transpiration, while the exposed lower surface is protected 

 by the strongly developed cuticle. 



In the marsh form of this plant, the stomata are chiefly on the lower surface of the 

 leaf, thus indicating less necessity for diminishing transpiration. The fresh leaves are 

 thicker than those of the ordinary savannah form and have a somewhat fleshy, almost 

 spongy, texture. It is remarkable that this is caused mainly by an increase in the size and 

 number of the water conducting vessels of the xylem, annular, pitted and reticulately 

 thickened vessels, with large lumina, being noticeable in the nerves, while there is no 

 marked development of special aerating arrangements, such as large intercellular spaces. 



The stolons of the ordinary savannah form show in cross-section, commencing at the 

 exterior, (1) Epidermis with thick cuticle, (2) One to two layers of sub-epidermal scleren- 

 chymatous fibres, (3) A thick sheath of parenchyma, the walls of which turn purple with 

 chlor-zinc-iodine, (4) A small central woody cylinder containing the vascular bundles. This 

 cylinder is protected by an outer layer of thick sclerenchyma, while the bundles are also more 

 or less completely surrounded by sclerenchyma. The walls of the tissue of this inner 

 cylinder all turn dark yellow with chlor-zinc-iodine, with the exception of those of small- 

 areas of parenchyma found chiefly in the centre, which turn purple. 3 The stolons of the 

 swamp form show an essentially similar structure with the remarkable exception that large 

 air spaces are found in the outer parenchymatous sheath, thus indicating the necessity for 

 special aeration-devices in the subterranean stolons of the swamp form to enable the roots, 

 growing in poorly-aerated water-logged soil, to keep pace with the increased transpiration 

 caused by the enlarged leaf -surf ace and by the diminished protection of the stomata. 



1 See Grasses by H. Marshall Ward, 1S01, pp. 25, 62. 



2 See Brandis in Trans. Linn. Soc. London, Vol. VII, p. 73. 



3 The soft outer parenchymatous sheath (3) is often destroyed by vermin and stolons are often seen in which this sheath has been 

 entirely eaten away, leaving only the central woody cylinder (4) intact. 



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