250 



water. Generally only the distal two or three internodes remain green and 

 succulent, the more proximal portions of the shoots dry up and become thin. 



Arthrocnemum arhuscula often forms a pure community, though associated 

 with it may occur : — 



Kochia oppositifolia Suaeda australis 



Salicornia australis 



*The last two are prostrate half-shrubby plants; both occur most notice- 

 ably at the seaward margin of the thicket. K. oppositifolia is a low bushy 

 plant, about 50 cms. high. It occurs scattered over the Arthrocnemum arhuscula 

 zone. 



The soil analyses (Nos. 1 and 2) show that the above plants are true salt 

 marsh species, being able to live in a muddy soil that is constantly wet and with 

 a high saline content. In spite of these factors the plants of this consocies 

 appeared turgid and healthy, much more so than those of the communities further 

 inland, which were showing the effects of the prolonged drought. 



Arthrocnemum halocnemoides consocies. 



A dwarf shrubland in which Arthrocnemum halocnemoides is the dominant 

 occurs as an open community over the greater part of the coastal plain. The 

 ground is flooded occasionally at high-water spring tides, but during the wet 

 season it is frequently swampy owing to drainage. 



The soils of this area are Nos. 4a and 4b, 5 and 7. Excluding for the 

 moment No. 5, it will be seen that the moisture in the soil as collected ranged 

 from 218-11 8 per cent. The total salts in the air dry samples range from 

 4 9-2 9 per cent., of which 3'77-2'30 per cent, is sodium chloride. The organic 

 matter is low, while the lime, owing to shell debris, is high. 



A. halocnemoides forms a pure community near its seaward limit. Further 

 inland Frankenia pauciflora and M esem,hryanthemum, australe appear between 

 the scattered bushes of the samphire. The surface of the soil here is light and 

 powdery ; the surface layer is analysed as No. 5. This soil, which extends to 

 a depth of about 7 cms., was practically air dry when collected. The content 

 of soluble salts (72 per cent., of which 5'33 per cent, was sodium chloride) is 

 much higher than the underlying layers. This surface layer miay be said to 

 have its own flora of shallow-rooting plants, the Frankenia and Mesembryan- 

 themiim mentioned above. Their roots were not observed to penetrate the 

 deeper layers, nor do the roots of A. halocnemoides develop in the surface layer. 

 It is almost as if two different habitats were superposed in portions of the plain. 



Arthrocnemum halocnemoides is a low shrubby perennial, here generally 

 under 50 cms., with a free branching habit. The internodes average 2 cms. in 

 length and remain fleshy for some distance down the shoot, so that the plant has 

 a much greater water reserve within its tissues than has A. arhuscula. The! 

 old stems may attain a thickness of 3-4 cms. at the base, but have a charac- 

 teristically brittle nature owing to the structure of the "secondary wood." 



The root system is of interest. There is a short tap root and several lateral 

 branches that descend nearly vertically for 18-20 cms. There they meet a stiffer 

 clay svibsoil, along which they run horizontally, branching freely. They do not 

 penetrate the subsoil themselves, but bear at frequent intervals much thinner 

 lateral roots. These are under 1 mm. in diameter, do not become secondarily 

 thickened, but obviously function only for a limited time before they die. They 

 are replaced by other roots arising close to their bases. These in turn die and 

 are replaced, so that tufts of rootlets occur along the horizontal roots. It seems 

 probable that this "deciduous" root production is associated with alternating 

 periods of vegetative activity and quiescence. A somewhat similar production of 



