WATER-GLANDS IN THE LEAF OF SAXIFRAGA CRUSTATA. 413 
neither hairs nor endodermis. The protoplasm is not nearly 
so granular, neither is the activity of function so great. 
Between the glands of the Saxifragacee and Crassulacee 
and those occurring in the rest of the vegetable kingdom, 
there appears to be a great gap. We look in vain for the 
well-differentiated gland and the conspicuous difference 
between the gland-cells and the adjacent parenchyma. 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, indeed, even in its most 
differentiated form, it is but a modification. 
It is interesting to note that the diminution of gland-tissue 
is often accompanied by an increase of fibro-vascular tissue, 
which appear to replace it. Comparing, for instance, Saz- 
fraga crustata and Crassula arborescens, the reticulated 
cells at the base of the gland are much more numerous in 
the latter than in the former, and this seems to be a general 
tendency in the less highly differentiated glands. 
As to the position of the glands, it seems to be a rule 
that they occur on the margin of the leaf. The exceptions 
to this statement are afforded by Crassula cordifolia, Crassula 
arborescens, and Crassula portulacea, where they occur dis- 
tributed over the surface. In leaves with an entire margin, 
they usually occur only at the apex, z.e. the extremity of 
the main fibro-vascular bundles, as in species of Azalea, 
Myosotis. In leaves whose margins are cut or indented 
there may be a gland at the apex of each tooth, as in 
Primula sinensis, Fuchsia globosa, Alchemilla vulgaris, 
between two teeth, in the indentation, as in Crassula 
spathulata, or even on the sides of the tooth, as in Senecio 
petasitis. 
In species of Sazifraga they appear to occur only on the 
upper side of the leaf. In Crassula lactea and Crassula 
coccinea on the upper and under margin, and in Sedum 
Sieboldit only on the under side. 
The number of water-pores in relation with each gland 
varies very much. In Sazifraga crustata 2—3, Bryo- 
phyllum calycinum 5—6, Crassula coccinea 1—3, Crassula 
spathulata 15—20, Crassula lactea 15—18, Primula sinensis 
1—2, Hordeum vulgare 1—2. 
In by far the larger number of plants the activity and 
life of the water-gland and structures analogous to it appear 
to be co-existent with that of the leaf as a whole. In 
certain cases, however, e.g. species of Musa, Richardia, and 
grasses, in which the gland is borne at the apex of the leaf, 
