Cooke. — Observations' on Salicornia australis. 355 



Aqueous Tissue. — The cells are large, thin-walled, and colourless, and 

 have a delicate lining of protoplasm. The nucleus is large and well marked, 

 and the remainder of the cell is filled with water. 



In a plant whose cells have remained succulent all the winter the water 

 has much salt dissolved in it, and chloroplasts are found in the protoplasm. 

 Starch-grains are present, and are often aggregated round the periphery 

 of the nucleus. 



In plants grown under a bell jar through the winter all the aqueous 

 tissue contained chloroplasts. It may be inferred that the aqueous tissue 

 is modified chlorenchymatous tissue. 



Palisade tissue is developed on the ventral side of the leaf and leaf- 

 base. The tissue is two or three cells deep. The cells are thin-walled, 

 elongated at right angles to the epidermis, have rounded ends, and are 

 separated by numerous small intercellular spaces. Large intercellular 

 spaces, respiratory cavities, lie beneath the stomata. 



Palisade-cells contain numerous chloroplasts, and, with the exception 

 of the guard-cells and aqueous tissue in the case mentioned above, they 

 are the only cells containing chlorophyll. 



The chlorenchyma is interrupted at intervals by small patches of water 

 tissue two or three cells wide, and in these patches are sometimes found 

 the scattered tracheides. 



Palisade tissue is not found in the stem itself. 



A longitudinal section of the growing-point shows palisade tissue well 

 developed about the 6th or 8th leaf down. Further down it is to be seen 

 developing from an intercalary growing-point. 



Scattered Tracheides. — These are present in the palisade tissue of both 

 leaf and leaf-base. Their length is perpendicular to the epidermis, but 

 they do not reach out to it, ending one short cell from it. There are a 

 number of these short palisade-cells, but they do not form a layer. The 

 other end of the tracheides abuts on the water tissue, but there is no con- 

 nection with the vascular bundles there. According to De Bary (1, c), these 

 tracheides occur close to one of the numerous air-cavities of the stomata. 

 1 also found them in the water-containing palisade tissue in the leaf, and 

 in such cases they were two or three cells from the epidermis. The tra- 

 cheides are cylindrical in shape, the ends being sometimes oblique. The 

 walls are thicker than those of the adjoining cells. Thickening takes the 

 form of a close fine delicate spiral. The function is that of air-storage. 

 Similar air-storing tracheides are referred to in Salicornia herbacea by 

 Ganong (3, a), and by Duval Jouve in Salicornia emerici (see fig. 4, a). 



Apical Growth. — A longitudinal section through the apex of the stem 

 shows an apical cone surrounded by leaves. It appeared as if the opposite 

 character of the leaves was a secondary consideration, since the leaves 

 were at the very apex alternate. This was probably due to the twisting 

 of the young stem, since cross-sections did not bear out this theory. 



The meristem at the apex is differentiated into three layers — (1) the 

 outer dermatogen. a layer of cells all the same size with mitotic nuclei ; 

 (2) periblem, two or three cells wide ; (3) plerome (see fig. 3, a). 



There is a slight bulging in the apical cone where the next leaf will arise. 

 The leaves overarching the growing-point are wider at the apex ; the other 

 leaves taper to a point (see fig. 2). 



There is a depression in the leaves on the lower side, and in this 

 depression the apex of the leaf next below lodges. 



Stomata do not appear to be formed till the 4th leaf down. 

 12* 



