Page:The Journal of Indian Botany.djvu/260

222 THE JOURNAL OF INDIAN BOTANY. distension of the stalk whereas the one in Crone's solution responded to the medium and appeared with bladders of the intermediate type already shown above. It was also noticed that the absorption of water from the dilute solution was so enormous that after a warm day when the Temperature suddenly cooled down from 86°F at 3 P.M, to 76°F at 5 P.M. there was copious exudation of water from the apex which was not the case in the other two plants. It may, in this connoction, be pointed out that the function of the apical gland appears to be rather to serve as a hydathode than as an absorbing organ as maintained by Goebel (2).

Anatomy: — As an effect of this high-water content notable changes are brought about in the growth of the leaf stalk. The turgidity of the cells is maintained by a high hydrostatic pressure which leads to the dilution of the cell sap as evidenced by the fact that - the cells plasmolyse readily with a 1/5 normal solution of potassium nitrate, whereas this concentration is only just enough to overcome the rigidity of the cells in the long stalked leaf. The living cells of the leaf stalk thus become so much gorged with water that a plastic stretching of the cell walls ensues due to superficial growth, and as the cells of both transverse and vertical layers are subjected to this process the stalk assumes a spherical distension comparable to an inflated bladdcler, and is filled with numerous polyhedral chambers bounded by layers of thin-walled cells (diaphragms) in an extremely stretched condition. Owing to this plastic stretching from the beginning the intercellular spaces in the diaphragm are considerably reduced and are practically confined to the periphery. Against this may be contrasted the structure of the bladderless stalk. This shows numerous air cavities which are partitioned by diaphragms but these are pierced by intercellular spaces from the earliest stage which points to the absence of any stretching due to turgidity. The intercellular spaces arise by the separation from each other of the walls of the diaphragms cells at several points and the air cavities communicating in this way evidently facilitate rapid diffusion of gas from the aerial organs to the root-system which is badly aerated, being fixed in mud or under other conditions referred to below. In the bladdered leaves, however, the diffusion of air contained in the chambers must be a slow process occurring only through the cell walls as the cavities do not communicate with each other. The presence of needle shaped crystals of calcium oxalate in considerable amounts also suggests the previous formation of oxalic acid which probably maintains a high osmotic pressure owing to the peculiar conditions which lead to the diminished water content. The principal changes in the anatomy are shown below:—