OUR NATIVE FLORA.

Auckland Star, Volume LV, Issue 224, 20 September 1924, Page 24

OUR NATIVE FLORA.

A BOTANIST'S JOTTINGS. AN ILD-OMENED PI.AKT. (By 3IARGUERITE W. CEOOKBS, M.A.) Spring is with us early this year, and under the influence of the milder i weather, life in its thousand forms is ; stirring again in the bush and by the ! seashore. One ehrub or tree which we shall find particularly active at this time of the year is the well-known, not to say notorious, tutu (Coriaria Tuscifolia). The tutu varies a good deal in size and habit, but it is very common, particularly round about the seashore. Perhaps one reason for its commonness is that it is extremely adaptable. It may be a shrub a few feet high, or, if it I finds circumstances favourable, it may ibe a tree of "about twenty-five feet. Under any conditions, however, it is generally straggly and untidy in its i method of growth. Its leaves are from one to two inches long, dark green and glossy and come out exactly opposite each other on the stem. However, it is not the leaves of the tutu that claim our attention just now, but the flowers. jNotothat they are particularly beautiful I —but what they lack in size they make !up_in_ abundance and interest. These tiny inconspicuous green blossoms are produced in vast numbers all around j pendulous flower stalks, sometimes seven or eight inches long. Even when the plant is in full bloom the flowers are not particularly noticeable. But aa the long flower stalks hang down heavy with their collections of flowers, they are susceptible to the breath of every passing wind, and thus they are easily accessible to the unseen agent that aids them in the production of the 'next generation. For it is the wind, not birds or insects, that carry the pollen from flower to flower, thus cau3----i ing fertilisation and enabling the plant to carry on its work of seed-making. The Wind as a Helper. Now the method of utilising the wind instead of insects or birds, though it works very well in some cases, is a . somewhat old fashioned manner of pro- | cedure. It is no longer used by the {dominant and most highly specialised members of the plant community. It was indeed considerably more fashion{able in the plant world a few million years ago than it is to-day. ■ On the other hand it must be admitted that the wind as a pollen carrier has several advantages. For one thing, like the poor it is always with us. Moreover it works for nothing. It needs no bright colours or sweet scents to attract its attention, nor need the flower manufacture honey or other pleasant juices to induce it to enter. On the other hand, it has .great 'disadvantages. It is immensely and inevitably wasteful, and scatters vast quantities of pollen dust to no purpose. Now with insects it is quite different. The plant must take an immense amount of trouble to attract the insect, but when the visitor has once arrived there is every chance that it will convey the pollen, with which the flower smears it, to another flower -without delay. When, however, the wind is the plant's ally in this matter, the chance of any particular pollen grain reaching exactly the right part of another flower of the same species is distinctly small. For every grain that safely reaches its destination there are many thousands that come to grief by the wayside. Therefore in order that any shall reach the- right place at the right time, the plant must have recourse to -manufacturing the grains in enormous quantities. Now we find all the characteristics of wind-pollinated flowers illustrated at the flowering season of the tutu. For each of these tiny blossoms bears an organ for producing pollen and also an organ with a sensitive part that receives the pollen and is fertilised by it. But if we examine the tutu flower we see 'that both these parts do not ripen at the same time. That would never do,' for if it were so the receptive part might be pollinated by pollen from the same flower and unhealthy offspring would result. Consequently the pollen-receiving parts ripen first. A stalk that divides into five little sticky branches protrudes out of the flower. In addition to _bejng sticky, the branches are .covered with minute hairs- so as to make doubly sure of entrapping any wandering grain of pollen. ifrtien tne y have been exposed long enough to give them a reasonable chance of being fertilised by pollen from an older flower they wither. But while they wither, "the pollen-bearing parts start to grow. When they are mature they protrude out of the flower so that the quantities of pollen they bear may be freely exposed to every passing wind. Mischief Working Seeds. When the business of shedding and receiving pollen is over, seed-making is the order of the day. As this process continues, a curious change comes over the flower. It usually happens with plants, that during seed making the floral leaves wither. But with tutu it is different. Instead of withering the petals or floral leaves take on a new lease of life. They enlarge, become filled with a purplish juice, and act as a protective envelope for the tiny seeds. The seeds themselves, like the green shoots, contain a deadly poison. Nevertheless, the Maoris with that ingenuity that characterises mankind generally in the manufacture. of refreshing drinks, succeeded in producing quite a pleasant beverage from- the berries by straining out the seeds. The poison contained in the seeds and shoots of tutu has in the past been the cause of considerable loss to farmers. - On the other hand, the effects of the poison have probably been exaggerated by allowing overdriven stock to feed on the plant. Mr. G-. M. Thomson says "animals when taken quietly on to tutu-covered ground and allowed to feed there got into fine condition, even when they ate it freely." But he adds if a mob of cattle that had been driven all day were put on such ground, "many of them used, to go mad during the night," and often some would be lost.

"After Many Wanderings—" Perhaps the poisonous properties of tutu have stood it in good stead, for it certainly belongs to a very •'Jongestablished family. And the former wanderinge and migrations of the familyto .which it belongs give rise to some very interesting speculations. Tutu belongs to the Coriaria family, which occurs in Southern Europe, Japan, China and the Himalayas. Two members of the family in South America belong to the same species as our New Zealand tutus. The occurrence of these two identical species in countries so far apart as New Zealand and South America separated by wide stretches of impassable ocean is very puzzling. Mr. G. M. Thomson suggests a solution of the problem on these lines. An incredible number of years ago, in a former geological age, when the temperature of the earth was quite different from what it is now, and

the climate of Spitzbergen was mild and temperate, the Coriaria family flourished in the extreme north of the Northern Hemisphere. But with the close of' one of the great glacial epochs the great icecaps began to settle round the North Pole, driving the vegetation southwards. Now the Coriaria family, thinks Mr. Thomson, retreated in two different directions. One direction lead it southward to Southern Europe, where it eventually settled. Some members of the family, however, "made off" in another direction. These retreated, first through the Behring Sea. Continuing south, one branch of the family went west, passing down through Japan and China to the Himalayas, where it "called a halt." The other branch to -which the two South American and New Zealand species referred to belonged, went east, passed down the mountain chains of South America, across the Pacific by land connections now submerged, finally forming its southermost outpost in New Zealand. Whether this is the true account or not of what happened, it is of course impossible to say, but it is certainly a feasible suggestion supported by much scientific evidence.