Cross. — Observations on some Neiv Zealand Ilalophyfes. 573 



are said, to function as hydathodes (v). Stomata arc rather large, and 

 occur on both surfaces, this last observation does not lend support to 

 the generally accepted view that halophytes exhibit a xerophytic structure. 

 Chrysler (xiv, p. 463) also notes the presence of stomata on both surfaces 

 in maritime plants. However, this may be due in some cases {i.e., Atri- 

 plex) to the more or less vertical position of the leaves. Again, in very few 

 instances are stomata sunk beneath the general surface of the epidermis ; 

 but it would be unreasonable to argue from this that these plants do not 

 show a xerophytic structure, as even the most typical xerophytes do not 

 exhibit every single one of the strictly xerophytic adaptations. 



Mesophyll shows the following characteristics : (a.) A great develop- 

 ment of palisadic tissue, a remarkably xerophytic character, resulting in 

 the checking of too rapid transpiration. (6.) A corresponding reduction 

 of the spongv parenchyma, (c.) In some cases a development of a definite 

 water-bearing tissue (Cotula coronofijoUa, Selliera, and the stems of Sali- 

 cornia). {d.) A great reduction of the intercellular spaces ; and no doubt 

 to this is due the translucence of the leaves ; this reduction causes a 

 diminishing of the transpiring surface, (e.) In some cases chlorophyll 

 grains are few ; by experiment it was found that the size of the grains, 

 rather than their number, increased when plants were cultivated away 

 from their native habitat. (/.) The vascular system is not particularly 

 well developed, {g.) A definite endodermis is almost invariably present, 

 as Brick, wto calls it the " starch-sheath," found in many maritime plants. 



Origin of the Halophytic Formations. 



Many of the above characters are plainly those of xerophytes, the main 

 object being to reduce the transpiring surface. Cotula coronopi folia, how^- 

 ever, shows scarcely any of these xerophytic characters, for it has no true 

 palisadic tissue in its leaves, and it has large intercellular spaces in both 

 leaves and stem. This latter fact, above all, would lead to the conclusion 

 that this plant was primarily an acjuatic plant, able to frequent brackish- 

 water pools, and that from these it has crept up into the meadows, 

 where it has undergone a few modifications, such as the formation 

 of a water-bearing tissue, to cause it to flourish as it does in its new 

 enxnronment. 



Again, Plagianthus certainly exliibits characters essentially xerophytic, 

 and is of a type very similar to typical New Zealand xerophytes {i.e., 

 Coprosmas). The question to be considered here is whether its xerophytic 

 characters are to be regarded as results of a direct adaptation to its present 

 environment, or whether, primarily a xerophyte. it found those modifica- 

 tions which fitted it for its life as a xerophyte equally useful in its new 

 surroundings. If this latter supposition be correct, it may be said that 

 these halophytic formations have a threefold origin — i.e., from hydrophytes 

 {Cotula coronopifolia). xerophytes, and lastly mesophytes, for many of 

 them are to be found inland in typical mesophytic formations {Cotula dioica, 

 Selliera radicans). Schimper, however, defines halophytes as " salt-enduring 

 xerophytes driven to the shore by competition." In any case, we must 

 agree that these are very probably " ordinary inland plants which have 

 been driven out of the more hospitable ground by better-equipped com- 

 petitors," and that they " occupy their peculiar station not from choice, 

 but from necessity" (xix), for when transferred to ordinary soil they grow 

 luxuriantly, while many are found inland. 



