NATURE NOTES.

New Zealand Herald, Volume LXVI, Issue 20366, 21 September 1929, Page 1 (Supplement)

NATURE NOTES.

" WET " AND " DRY " PLANTS.

BX J. DIItJIIMOND, F.Z..5.1 F.Z.3.

There are " wets" and ° drys" among plants as well as among humans. Some plants aro so fond of water that they spend all their lives in it. A typical New Zealand plant in this group bears the namo, in Greek, of Myriophyllum, meaning a thousand leaves. li is not many leaved, but ils fo'iagc is deeply cut. Although it submerges itself in ponds and streams, it raises its white flowers to the surface. Tho bladderworts. herbs that livo and float in water, are among the plants most famous for excellent adaptation to environment. Their flowers, yellow, white or purple, aro floated by tiny bladders to the surface, in order to ensuro pollination. Serving a doublo purpose, tho bladders entrap small creatures, by tho plants for food.

The opposite group, the " drys," which love drought and dry conditions, aro very well developed in New Zealand. Some of them have reached an intense-special-isation of structure in seeking dry conditions. So marked is this that a German botanist was led _to compare the physiognomy of plants in New Zealand s sub-alpine pastures to tho physiognomy of plants on the steppes of Persia, which are almost rainless. Iho spiny Wild Irishman, which favours stony plains, sand dunes, and clayey hil'sides, proclaims its love for droughty surroundings by its small leaves, which are very few, and by its hard, narrow, pointed shoots. Studying tho Wild Irishman's development, Dr. L. Cockayne, 6f Wellington, by experiment, found that, originally, it was spineless, and had small, thin leaves, adapted to moist conditions. In those remote days, perhaps, New Zealand s climalo was.much moister than it-is now. It became drier slowly. The Wild Irishman changed accordingly, its structure to suit tho changing environment.

In natural conditions, a seedling Wild Irishman is erect, leafy and spineless. It is prepared to meet moist conditions. When an infill or two inches high, it begins to develop spines; and its leaves are fewer, some being thrown off. A Wild Irishnjan in that stage, while adapting itself to drier conditions, was placed by Dr. Cockayne in a warm, moist chamber It ceased to develop spines: it retained its leaves; '!t returned in response to tho stimulation of warmth and moisture, to its seedling form. Tho Wild Spaniard, with its long, swordlike, spiny leaves, attracted the attention of early New Zealand botanists, who believed that this plant's spiny adaptations, like Ihe spines of the Netful porcupine, were designed for special protection from grazing animals. Tlipy were puzzled to account for a plant arming itself in this terrible way in a countrv that had no grazing animals until Europeans came. Dr. A. R. Wallace suggested that tho Wild Spaniard may have equipped itself in this way to preserve itself from being trodden down by moas. •

The opinion now is that the Wild Spaniard's spines are not for defence against enemies but to fit in with drought conditions. As a matter of fact, the spiny leaves do not save the Wild Spaniard from slock. It soon disappears where stock are run. Sheep and cattle eat the young plants, and there are none to replace old ones that ciie. Rabbits can, and do eat single leaves without being pricked or spiked by other leaves, and so they destroy mature plants. _ On the whole, the well-armed Wild Spaniard, bristling with bayonets, is not as formidable' as he looks.

Plants in this group—they are xcraphytes; that is, dry plants—have adopted several means to enable them to exist, under dry conditions. One of these is reduction of the rate of evaporation from leaves of tho water they have absorbed. This is done by obstructing evaporation through tiny pores on the outer skin of leaves. Each pore is surrounded by a pair of guard cells. By changing their forms these cells open or close a pore, and regulato the evaporation. If evapoiation is dangerously liberal, the pores are closed until further orders. Peculiarities of structure, on which tho obstruction of a pore depends, often are described in botanical text books as if they characterised tho xerophytes generally; but many of these plants are devoid of appliances for obstructing free evaporation. When sufficient water is available, they trans piro more copiously than ordinary plants Some of them cover their loss of water by a very richly-branched system of roots, or a deeply-penetrating one, by which they can tap a large bulk of soil or go down to very deep layers. Others store large quantities of water absorbed by them in a short, rainy season, and lose it by evaporation very slowly.

As a class, f6rns are lovers of mois-, ture; they usually prefer tho shade. Most have specially adapted themselves to those conditions. Yet many endure exposure to tho sun's strong rays, and, as slated, even to temporary drought. The limit of this unusual development seeins to bo in ferns of tho Old Country that grow on rocks, or on tho dry tops of walls. In the summer their leaves sometimes aro dried to a crisp. By their adaptations, they tolerate those places and seem even to like them.

Mr. A. 11. Chisholm, of Sydnoy, has a much wider field of study than New Zealand ornithologists enjoy. _ Somo of New Zealand's birds—tho kiwi and the weka, for instance —are more inte-esting than any birds Australia can produce, but tho Commonwealth has incomparably more species of birds than the Dominion has, and, perhaps, greater variety than any other country in tho world. With a long experience, a gift for observation, and hound I ess enthusiasm, Mr. Chisnolro, in "Birds and Green Places," has given his intimate rich knowledge, or. at least, a large measure of it, to the public. Hp has done so in an attractive way that makes acquisition of the information he has supplied an easy and pleasant process. His book is an introduction to Australia's bird-life gene-ally. Its ranee is from the kiwi's family connection the emu, to tho darling fan!ails, warblers, and honeyeaters. Symmetry, sweolness and airiness of voice, charm of environment and ancient lineage are the qualities Mr. Chisholm ascribes to tho Australian warblers, which have a New Zealand representative in tho plaintive-voiced, crev costumed, modest, anxious litt.lt> bird that builds wonderful domed nests, and often rears in them parasitical cuckoos. The warblers appeal to Mr. Chisholm as the most endearing birds. The same adjective may be used for tho grey warbler of New Zealand.

" About two weeks ago," a Christchurch correspondent wrote on September 9, " I climbed the branches of a ha2el tree and found an old nest, which, from its appearance, I believe was a songthrush's. It was somewhat weather-worn, and it was in my mind to pull it down, but I did not do" so. The following day, while I was working near the tree. I heard the flutter of a bird flying away. Climbing up, I found three greenish.blue, dark-spotted «ggs in the nest. The nest had been repaired, the lining being patched and a quantity of fresh dried grass placed round the outside. Bearing in mind the adage that ' there are no birds in last year's nest,' I was surprised to find an old nest being used again. Is this usual? I never knew it to occur i before."