8 4 



spicuous difference between its cells and those of the adjacent 

 parenchyma no longer occur ; in fact the gland cells and the 

 parenchyma appear to merge into each other. In Alchemilla 

 the spiral cells terminating the bundle are simply continued to 

 the surface of the leaf, and there is no proper gland tissue at all. 

 But the water-pore long preserves its individuality, although 

 in many cases it seems probable that its function is taken on 

 by an ordinary stoma of which it is, even in its most differ- 

 entiated form, but a modification. The number of water-pores 

 in relation with each gland varies very much ; there may be 

 one or a group, thus — 



In Saxifraga crustata, i — 2 — 3. In Primula sinensis, 1 — 2. 



Bryophyllum calycinum, 5 — 6. Crassula lactea } 15 — 18. 



Crassula coccinea, 1 — 3. Hordeum vulgar e, 1 — 2. 

 Crassula sj>atkulata, 15 — 20. 



In Primula sinensis the water-pores lie flush with the leaf 

 surface. If we cut off a leaf and place it in water, the secretion 

 of fluid in the form of drops of water will cease. If we take 

 a whole plant of Alchemilla vulgaris and plant it in a pot, 

 when the amount of transpiration from the leaves is very great, 

 and consequently there is no evident root pressure, the excre- 

 tion of drops of water by the leaves will cease ; but if we 

 place the plant under circumstances by which the amount of 

 transpiration is diminished and the evident root pressure in- 

 creased, we get drops of water secreted. These last-named 

 conditions actually take place in nature, as we may see by 

 considering what occurs in a small specimen of this plant 

 through the space of a day and a night. At night transpiration 

 is almost absent or very much diminished, while the root ab- 

 sorption is very active ; hence the water accumulates and fills 

 the vessels, thus giving rise to a root pressure which is so 

 considerable that it fills all the vessels of this low-growing 

 plant with water, and hence if we examine the plant in the 

 morning before the sun has got to it we shall see large 

 and numerous drops of water fringing the edge of the leaves, 

 which are secreted or forced out by the water glands, and have 



