THE NATURE COLUMN.

Southland Times, Issue 17010, 6 April 1912, Page 11

THE NATURE COLUMN.

iOoaduoted by “STUDEHT,” to whom all Ooauanaioatloßi most be Addressed). will be pleased to receive notes on any branch- of Natural History. Observation of birds. Insect*, plants, «tc., whether native or Introduced, will be equally welcome. Correspondents must use only one side of the paper and, If using a pen-name must enclose both name and address. SHE STRUGGLE FOB LIFE. Dear Student,—While taking a lesson on the Native Flax (Phormium Tenax) to-day, I was struck by the number of small grubs—evidently the larvae of some fly—which appeared to be living in a very healthy condition in some of the pods. There were a great many of these grubs In one pod and as they must exist on the seeds, this probably accounts for the fact that so few of these seeds germinate. We counted the seeds in one cell (the flax has a three-celled seed vessel) and found it to contain over sixty seeds, making an estimate of ISO for each pod. Now, as there are anywhere between 50 and 80 of these pods on a single korari, and 10 or more koraris on one flax bush, there must be some reason for so few of the seeds growing into plants. I am hoping that you, or some of your readers will be able to tell me if these Insects are natural enemies to the flax, eating the seeds in order to prevent Its over-running the country. The eggs from which the grubs are hatched must have been placed in the flower by some fly or moth attracted to the flowering korari by its bright colour or by the feast of honey offered. If the latter, it seems a poor return for the kindness received. I am trusting that I will be enabled through the medium of your column to ascertain the kind of insect which placed the eggs in the flower, or that I may be corrected if my opinion of the matter is erroneous.—Yours trulv. “ curious!” I am especially pleased to receive the above letter. In the first place It is from a school-teacher, a member of a profession which I want to get into close touch with. In view of the fact that the teaching syllabus provides for a considerable amount of nature knowledge there Is no doubt but that teachers, in dealing with this portion of their duties will meet with many facts of interest to Eature students In general. This column will always be open to receive any information which the members of the profession may have to communicate, and at the same time the writer will in his turn be pleased to give any assistance in his power In the way of naming specimens or giving notes on habits and affinities. In the second place the letter Is more than ordinarily welcome because the writer Is the first lady who has sent a note to our column. I hope that the example of “Curious” will be soon followed by other lady correspondents. In the absence of specimens I am unable to give any definite information regarding the grubs found among the flax seeds. The flax plant is attacked by a number of different pests, but I should think it probable that the present larvae belong to one of the diptera. or twowinged flies. If "Curious” will send me a flax pod containing some of the larvae I will endeavour to give some further notes. Our correspondent’s calculation of the average number of seeds produced by a flax bush opens up an exceedingly interesting subject. Taking ISO seeds to each pod, and 60 pods to each karori (flower stalk) and say, 5 koraris to each plant, we arrive at the startling total of 54,000 seeds to a single bush. Now, for the flax plant to hold its own it is not really necessary for it to produce seed at all as the growing clump is continually sending up fresh young shoots to take the place of the exhausted older growths. But, so careful of her children's welfare is Mother Nature, that in addition to this method of growth she provides thousands of apparently needless seeds as well. It may be accepted as a natural law that each plant or animal produces just sufficient progeny to enable it under ordinary circumstances to keep its numbers up to a certain definite level. Though many species tend to swamp out all other competitors they are kept within bounds as long as normal conditions prevail, but if some ciiange occur which favours their increase then they sweep all before them until they, in turn, meet with some check, and the balance is once mere adjusted. But the case of our native flax is a very ordinary one in comparison with many other organisms. In a recent lecture Professor J. A. Thomson gathered together some of the most striking examples of fecundity in nature and they are indeed astonishing. A common British need (Sieymbrium Sophia) often has tbreof-uarters of a million seeds; if all grew to maturity for only three years the whole of the land surface of the globe would not hold them. An annual plan! with only two seeds would be represented by 1,048,576 in the twentyfirst year. A cod has two million eggs; If these all developed into cod there would soon be no more fishing. An American oyster produces on an average sixteen million eggs. If all the progeny of one oyster survived and multiplied. It* ' great-great-grand-ch lldren would number 66 with thirty-three noughts after it, and the heap of shells would bo eight times the size of the world. If the descendants of a single green-fly (the aphis that attacks roses and other plants) all survived and multiplied they would at the end of summer, weigh down, the population of China. The common house fly lays eggs in hatches of 12b lo 150 at a time, and may lavfive or six of these batches during its life—of about three weeks in very hot weaiher. At the end of summer if all developed, and if there were six generations, the progeny of a single pair, pressed together into a solid mass would occupy a space of something like a quarter of a million cubic feet, allowing 200,0ut) flics lo a cubic foot. There is np real increase so the mortality must )M prodigious.

But it is when we come to the bacteria, those minute germs of life that only the higher powers of the microscope can reveal, that we meet with the most remarkable Instances of multiplication. Many of these bacteria are so small that 25,000 of them could be packed sideways In the space of an inch, yet the facts of their multiplication are almost too wonderful to be realised. Says Dr Saleeby, "The cholera bacillus can duplicate every twenty minutes and might thus in one day become six trillions with the weight of about 7366 tons. In a few days at this rate, there would be a mass of bacteria as big as the moon, huge enough to fill the whole ocean."

With so enormous a power of increase it is evident that there must be some effective check at hand or life would speedily multiply beyond measure and quickly fail for mere lack of room. That check Is the fact of the struggle for life. Every animal or plant exists more qr less at the expense of some other. Each struggles with its fellows —there is only sufficient food for a certain number and as that limit tends continually to be passed competition between the members of the same species is often very severe. Then, each species struggles with Its foes; natural enemies abound on every hand. Lastly, each species struggles with the inanimate forces of nature, with the frosts of winter. the droughts of summer and other conditions that the changing seasons bring. A set of conditions may arise which is extremely favourable to some form of life and as a consequence t'hat animal or plant multiplies at an altogether unusual rate. But its enemies, finding existence freed for the time from struggle, multiply also _and when the conditions swing back to the normal, competition again becomes keen and the, stream of life that has temporarily overflowed its banks is confined once more in its old channel. Now, if in the time of stress there arc some individuals of a species which, by reason of some variation in habit or structure, are hotter able to withstand the adverse conditions such individuals will have the best chance of surviving and rearing progeny. Such progeny will of course In a greater or less degree reproduce the favourable variations which enabled their parents to hold their own in the struggle and by the continued weeding out of the least-adapted forms the species, as a whole, will gradually but surely become better suited to the conditions which surround it. Tints, out of hunger, strife, and death is born progress and from the bitter struggle for life springs the beauty of perfect adaptation.