766 DOMATIA IN CERTAIN AUSTRALIAN AND OTHER PLANTS, 



in other parts of the leaf have little protoplasmic contents; but 

 over the dome they are riclier, and often contain chloroplasts. 

 From their varying appearance in leaves of different ages I 

 believe this layer is derived from the next below. 



(4) The palisade-tissue (6d} consisting of two rows of short 

 oblong cells, their long diameter being horizontal instead of 

 vertical. These cells contain many (up to seven) very large 

 chloroplasts. 



(5) A layer of spongy parenchyma (5/) containing also very large 

 chloi'oplasts. In this particular region this tissue can scarcely 

 be termed spongy, as it is composed of oblong cells laid over each 

 other like l^ricks in a wall; but away from the summit the cells 

 are branching and form the usual network, and the most open 

 part lies all round the perimeter of the cavity. The dense layer 

 over the roof is characteristic of the domatia in all the plants I 

 have examined. In the lamina, at a short distance from the 

 cavity, the intercellular spaces are arranged perpendicularly, and 

 extend from the lower epidermis to the palisade-tissue above, the 

 stomata opening as usual into the spaces. All through the leaf 

 in this region there are cells not to be distinguished in a fresh 

 section, but which stain veiy deeply with any stain, and more 

 especially with hsematoxylin, they become quite opaque before 

 the x'est of the section is sufficiently stained (5^). These cells are 

 very rich in tannin, and with ferric chloride give a greenish-black 

 reaction. There are also ducts in the vascular bundles of the 

 veins on each side of the cavity filled with the same substance. 

 The tannin-sacs are arranged in two parallel layers, one just under 

 the palisade-tissue, the other at the bottom of the layer of spongy 

 parenchyma, and resting on the inferior epidermis. All round 

 the domatia the two layers coalesce, and then open out again 

 the upper set going into the roof and the lower to the floor, and 

 extending right to the rim of the mouth. The lower layer is less 

 continuous, and thinner than the upper. 



(6) The inner epidermis of the cavit}?- (6(/) continuous with and 

 similar to the epidermis of the rest of the under side, but thinner. 



