absorbing water from it, which they do. These cells are also 

 of the nature of secreting cells, so that the water which they 

 absorb from the vessels of the bundle is poured by them into 

 the water-pore. The vessels of the fibro-vascular bundle do 

 not then open directly into the water-pore, but are separated 

 from it by the parenchymatous cells which form the secreting 

 gland, and the water is not poured into the pore directly from 

 the vessels as if from a pipe. In the day-time, when the tem- 

 perature is high and transpiration very vigorous, the secretion 

 of drops of water does not lake place, and even if water is 

 secreted by the cells of the glands, it is evaporated as fast as it 

 is secreted. But at night, when the temperature falls, causing 

 decrease of transpiration, the walls of the vessels, and even the 

 vessels themselves, become gorged with water, and every facility 

 for secretion by the gland is offered. Under these conditions 

 the cells of the gland become turgid, a pressure is set up, and 

 drops of water exude through the water-pores. As we have 

 seen, each water-pore is situated at the base of a depression 

 or pit in the leaf margin. The production of these pits is due 

 to cell division, though not to the growth of the cell, for this 

 practically ceases in the tissue of the water-gland with the divi- 

 sion of the epidermal cell into two to form the water-pore, 

 while cell division still goes on in the rest of the leaf, ending 

 only with formation of the stomata. The sides of these 

 pits, especially the outer side, i.e., the proximal side of the 

 lobe to the stem, — are lined or fringed with small, knob- 

 like, stiff hairs which are out-growths from the surface of the 

 epidermal cells which forms the walls of the depressions. These 

 cells, before the development of the pits, in the way above 

 described, formed part of the margin of the leaf. The hairs 

 are almost perfectly spherical, with very thick and highly 

 refractive cell-walls. The water which exudes through the 

 water-pores subsequently fills the pits, and as the hairs are 

 most abundant on the outer side, when an excess of water is 

 secreted and the pit overflows, this water tends to collect on this 

 margin of the lobe. This water is not simply water alone but 

 is charged with carbon dioxide gas, and holds in solution certain 



