gland, towards the fibro-vascular bundle, we find certain elon- 

 gated fusiform or spindle-shaped cells, with reticulate thicken- 

 ings on their walls, which cells are joined end to end, and even- 

 tually become continuous with the spiral vessels of the fibro- 

 vascular bundle. These cells present a series of intermediate 

 forms between gland cells with granular protoplasm and delicate 

 reticulate thickenings on the one hand, and the spiral vessels of 

 the bundle on the other, so that in the adult condition it is prac- 

 tically impossible to say exactly where the fibro-vascular bundle 

 ends and the true gland tissue (derived, as we saw, from the 

 the ground tissue) begins. 



At the broad end of this water-gland, where it underlies the 

 epidermis, we find one, two, or rarely three openings or apertures 

 freely communicating with the external atmosphere through 

 the epidermis: these are known as water --pores or water stomata. 

 Each of these resembles an ordinary stoma, in the fact that it is 

 bordered by two guard cells containing chlorophyll, which are, 

 however, derived from the division of a single epidermal cell. 

 These guard cells are larger than the ordinary guard cells of 

 the stomata, and the two together have a rounded contour as 

 compared with the elliptical shape of the pair of guard cells of a 

 stoma proper. The actual pore, moreover, is relatively smaller 

 than the opening of the stoma, and, unlike it, cannot be opened 

 or closed according to the degree of turgidity of the cells of the 

 leaf: — it is fixed, and always remains open. The time of de- 

 velopment is also much earlier in the case of the water-pores, 

 and their exact mode of development, as Gardiner has shown, 

 is quite different from that of the stomata; they differ also in 

 being confined to leaves only, whereas stomata, as we have seen, 

 occur elsewhere as well. The position of these pores in Saxi- 

 fraga crustata is on the margin of the upper side of the leaf, 

 at the bottom of each of the depressions or pits which occur 

 there. The mode of action of the whole apparatus is as fol- 

 lows : — Water occurs in the vessel-walls of the ultimate ending of 

 the fibro-vascular bundle (which, however, is completely closed 

 and blind); the cells of the gland in immediate connection with 

 which it ends are, however, parenchymatous and capable of 



