HYBRIDISATION

Evening Post, Volume CIX, Issue 92, 21 April 1925, Page 7

HYBRIDISATION

IN EVOLUTION

PR. LOTSY'S FINAL LECTURE

The third and final lecture of Dr. Lotsy's course was given at Victoria .College last evening. There was again » large and very appreciative audience of students of the college and of student members of the public. The chair was taken by Professor Kirk.

The lecturer began by reviewing the points already made—that the existence of mutation, that is to say, of a new character due to the gain of a, new factor in the germ plasm or to the loss of an old one, had not been proved; that variation due to hybridisation was abundantly proved, accounting for the appearance of new characters, the reappearance of characters that had perhaps been lost, and the disappearance of characters. In dealing with the part that hybridisation has played in evolution Dr. Lotsy had occasion to refer to his own very extensive series of experiments with many kinds of plants, and lie did so with v. reticent modesty that charmed his audience. Further elaboration was given to the ■view that when offspring differ from the parents, and that is practically always, the differences are not due to some physical change due to loss or gain of the material of heredity, but to an interaction between tho material supplied by the two parents; that the more nearly the two parents approach the homozygous condition, that is, the more nearly they are constituted alike for a _ given character, the less likely is variation to arise with regard to that •character. Of this all.breeders are practically aware, and hence the fancy prices they are prepared to give for pure pedigree stock. MUTATION THEORY. . No dogmatic statement can be mads that mutations have not occurred with the hybrid material that has been used in experiment by the advocates of tho mutation theory; only the statement that the occurrence of mutations has not been proved. To prove it, exact experiments must be made with cultures of proved purity; to obtain such cultures of proved purity may be difficult, nay even bo . impossible. That is the misfortune of tho mutationists, for without this preceding condition they can never furnish proof. Tho lecturer would no sooner deny that mutations may possibly have occurred in their experiments with impure material than he .would deny that spontaneous generation may have .occurred in unsterilised material} but while spontaneous generation is not proved to have occurred in the many exact experiments that have been made with completely sterilised media, there is no reason whatever to believe that it occurs in unsterilised media. It is admitted that the hypothesis of the existence of genes, that is to say, of actual particles of the germ plasm that bear some special character, has proved to be a. good working hypothesis. So was the conception of the atom when we were taught that it was a solid globule and no idea existed that it was a microcosm. Nature has practically cried out to us, "In each and every generation I give the opportunity for an exchange of qualities by means of sexual reproduction, and, consequently,, for the origin of. new forms. The diversity of your own children proves it: your gardeners^ and breeders: have'applied this principle for centuries, and were only able to keep the new forms that they produced in this way by isolating them in order to prevent new crosses. Such limitations I also impose, making use of isolation in space or in time, for instance, by difference in time of flowering, or by such absolute means as mntual sterility; but I never eliminate crossing from ray course, because, by so doing, I should cufc off the way to progession, io evolution. All of you have linown the anfluence of hybridisation, but every one of you has explained its influence away: only one of you, Kerner yon Marilaun, has clearly seen that new forms do not arise through the stimuli of the surroundings, but through the inHuence of sexual reproduction: and levenha was hot able to divest himself Entirely of the influence of universally accepted conceptions, so that he says .that, after all, the sperm whale might possibly vary under the influence of external conditions." PLANT EXPERIMENTS. j __ Investigating the results of crossing in antirrhinum by the careful propagation of the progeny produced as the result of a cross of two species, the lecturer had obtained 6500 different forms. •These had all segregated out, the potentialities for their differing characters having already existed unexpressed in the two original plants, or rather in the cross that made new combinations, new interactions of germ plasm possible. In crossing _ two forms a swarm of variations exist. In natural conditions most of v these would become eliminated, not being in any special conformity with their environment. In tho swarm Nature provides diversity, and from the diverse forms survivors are selected. And in the determination o£ survival the chance of position may have much to do, as it often has in determining the survivors of a, railway accident. In tho neighbourhood of Chicago tho sand dunes of Lake Michigan change and grow, coming to bury all kinds of trees and shrubs. Only those survive that are able to form new roots from their stems, otherwise the plants die because the supply of oxygen is cut off from their roots. Quito unrelated plants thus manage to grow upward? keepihg their leafy shoots above the surface of the dune and drawing food material from it by means of roots put forth from time to time at a suitable distance below the surface. It is commonly said that such plants survive because they have adapted themselves to their surroundings. But they already had in their constitution ■ the power to make the necessary "development,- unexpressed until 'the circumstances called for its expression. Had they suddenly been called upon to adapt themselves by means of a new modification it would have been too late, as it is too_ late for aYlrowning man to learn' to swim.

Members of the Cactacae and of the Euphorbiaceae inhabiting deserts have come to resemble each other externally in their succulent stems and their want of leaves, remaining in their other characters very distinct; a cactus remaining a cactus and n euphorbia remaining a euphorbia. But either plant may have succulent and leafless stems even in a moist_ climate. Thus in Java a species o! rhipalis retains these- characters in a moist forest of the tropics. If such a climatic change took place as would result in the transformation of Java into a desert, then doubtless these plants would survive, and all would say that they-had adapted themselves to desert conditions. • SUMMARY. Dr. Lotsy's views may be briefly summed us as follows: There is no such thing as mutation, that, is to saY". as transmissible' change brought "about, through Ih© influence yf._. eiivirouaieiit,

whether on the body plasm or on tho germ plasm. In this he is no less emphatic than is Weismann himself. What has been mistaken for' mutation is the segregation of characters brought about by the crossing of hybrids. This segregation may be brought about, not by the appearance of a new gene nor by the loss of an old one, but by the interaction of the germ plasm. The variations thus arising are not adaptive, and many of them are, in natural circumstances, eliminated. At the close of the lecture Dr. Lotsy was very heartily applauded. A vote of thanks was, on the motion of Professor Peren, seconded by Mr. Oliver, passed with cordiality. In acknowledging it Dr. Lotsy remarked that he had seen some very strange things in New Zealand, for instance, a cart which bore the legend, "Kea Butter and Kiwi Bacon." Almost this had made him a convert to mutation. The lecture was illustrated by lantern slides showing the results of the lecturer's own experiments, and by many coloured drawings. The chairman announced that the Canterbury College Council was printing Dr. Lotsy's lectures, and that it was hoped that Wellington would bo able to secure a supply, from which copies could be sold at cost price to those who handed in their names.