388 Groom . — On the leaves of Lathraea Squamaria 
of the dome-shaped glands, their close connexion with the 
tracheides terminating the vascular bundles, the separation 
of the latter from the upper face of the leaf, and finally the 
instantaneousness of the outflow, all pointed to the dome- 
shaped glands as being responsible for the excretion of water. 
It seemed possible that a careful examination of these latter 
might reveal some permeable spot in their cuticularized walls. 
Each gland consists of four cells arranged to form a broad 
truncate cone with both base and apex convex. The single 
basal cell is the largest, and bulges into the tissue of a leaf. 
Above it succeeds a single discoid stalk-cell. The two re- 
maining cells — the cap-cells — lie on the stalk-cell like two 
quadrants, roughly forming a hemisphere. The exposed walls 
of the gland are everywhere cuticularized, excepting at a 
circular spot in the centre of the apex at the junction of the 
two cap-cells. The cuticle is here interrupted by a large 
pore spanned by cellulose ; but inasmuch as the cuticle is 
usually slightly raised round the margins of the pore, the 
latter in lateral optical section looks somewhat like a unilateral 
bordered pit. The pore is often blocked by a little plug 
of mucilage, which frequently protrudes outwardly in the form 
of a minute rounded knob. This mucilage in many of these 
