HYBRIDISATION.

Otago Daily Times, Issue 19465, 28 April 1925, Page 4

HYBRIDISATION.

ITS ROLE IN EVOLUTION'. DK LOTSVS FINAL LECTURE. Dr J. P. Lotsy, the eminent botanist, delivered at the Museum last evening his third and ihinl lecture on certain aspects of evolutionary theory. This was iu many respects the most important and instructive of the three, containing a summing up of Dr Lotsy's particular beliefs, and in spite of the fact that the lectures are in no sense popular there. was another large attendance. Dr J. E. Holloway occupied their chair, and remarked that the dogmas of the old evolutionary theory were obviously now in the melting pot, and no one know how they would come out. This was a very startling and upsetting thing, but it was good that our fundamental ideas should be severely shaken from time to time so that we were compelled to re-examine them. A large number of explanatory pictures and diagrams arranged on the lecture desk were carefully examined beforehand by the audience. Dr Lotsy 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 now 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. He examined the method in which mutation was supposed to be proved, and showed wherein the proof was unsatisfactory. One gradually learned to see more and more differences in the material one was handling, and this led to the ascribing of small differences to mutational origin. He believed tjjat without a change in factors mutation would be impossible. He drew attention to the extreme difficulty of securing absolutely homozygous material. Mutation remained to him n meaningless term. It implied that a factor was able to remain what it was for a large number of generations, and then suddenly to change. Eor such a change there must oc a cause, and crossing seemed to be the most likely. He stressed the point that neither He Vries nor Morgan nor Bauer had caused in their experiments any of their material to mutate. It was admitted that the hypothesis of the existence of genes, that was to say, of actual particles of the germ plasm that bear some special character, had proved to be a good working hypothesis. So was the conceptoin of the atom when we were taught that it was a solid globule and no idea existed that it was microcosm. No dogmatic statement could be made that mutations had not occurred with the hybrid material that had been used in •jixr.eriment by the advocates of the mutation theory; only the statement that the occurrence of mutations had not boon proved. To prove it, exact experiments must be made with cultures of proved puritv; to obtain such cultures of proved purity might be difficult-, uiiffht even be impossible. That hub the misfortune of the inutationists, for without this preceding condition they could never furnish proof, lie did not r.ppose mutation. IKonly opposed those who claimed that the existence of transmissible variations had been proved. Ni'ture had practically cried out to us: "In each and tver.v 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," said Dr Lotsy. i, "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 bv isolating them in order te prevent new crosses. Such limitations I also impose, making use of isolation in space or m time, for instance, by difference in time of {lowering, or bv such absolute means i:s mutual sterility; but. I never eliminate crossing from my course, because-by so doing I should cut off the way to progression, to evolution. All of you have known rhe influence of hybridisation, but every one of you has explained its influence' away; only one of you, Kerner von Marllaum, has clearly seen Unit new forms do not arise through the stimuli of the surroundings, but through the influence of uexual reproduction; and even he was not able to divest himself entirely of the influence of universally accepted conceptions, so that he. saws, after all, the sperm might possibly vary under the influence of external conditions." Among all the controversies one fact stood firm. Hybridisation was able to create simultaneously a large number ol new forms, though the method was still mvstery. He. illustrated with large a.-.d sn'iall pictures many of the 0500 different individual forms he had obtained by the careful crossing of two closely allied species of antirrhinum. Members of the Cactaceae and of the Euphorbiaceao inhabiting deserts had 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 p euphorbia remaining a euphorbia. Their ossential characters had not been affected bv the desert climate. Uut either plant may have succulent, and leafless stems even in 'a moist climate. Thus, in Java, a species of rhipalis retains these characters in a moist forest of the Tropics. If such a climatic change took place ;is woulo resuit in the transformation of Java into a desert, then doubtless these plants would survive, and all would say that they hail adapted themselves to desert coir.iit.ions. It wm actually proved that loss of characters could occur by crossing and that now characters could arise from the same source. Ho controverted the well-know theory of slow gradual adaptation to surroundings by reference to moorland vegetation and argued that the peculiar properties which made certain plants thrive in peaty soil had not boon developed by living in peaty soil but had been tiioro all along. Many' of the lecturers notable experiment* were beautifully illustrated m series of coloured pictures which he handed round f.bo audience. Ho behoved that the frequency of cross fertilisation in nature was often underestimated. In a case ho had examined in Switzerland he found that M per cent of the possible hybrids ot a particular genus had actually been observed In another case he found 100 per cent, of the possible hybrids actually in existence. He quoted interesting examples of plants showing no variation until they mot, with other related species. The Queen Victoria plum was used to show what enormous variations in form of tree, of leaf, of bark , of size and colour of fruit could be obtained bv the self fertilisation of a single such olum tree. An important consequence of the thoorv of evolution by hybridisation was the possibility of the origin of the same form at different spots of the earth, the hybrid naturally arose- wherever the two parents responsible for its origin met. Dr Lotsy proceeded to consider the extent to which hvbridisation coolrl make its effects felt among animals. Limits there doubtless were, he admitted, though we did not know where to look for them In concluding ho drew attention to two factors on which his views wore based, cross fertilisation and one-sided maternal inheritance of the psycho plasm, liot.h of which were occurring daily everywhere. These-, ho believed, offered a firmer basis for evolution than anything else. He believed tnat all that was needed for the origin of species was cross fertilisation which produced variability. He considered this much simpler than the view of Darwin. At. the close of his formal lecture Dr Lotsy threw on the screen a number of slides illustrating many of his instructive experiments in fertilisation of tho antirrhinum and of other plants. Tho chairman confessed at the close that the first two lectures had been far beyond many of them, but they had nevertheless been most stimulating, and those who had heard them -would turn to these subiecte with fresh interest and enthusiasm. Mr TV. J. Morrell, a member of the University Council, expressed their great indebtedness to the lecturer. They all appreciated the fact, that Dr Lotzy bad put the subject with the utmost lucidity of which it permitted. If these lectures had meant so rrmch to the general public how much more must they mean to special students? The vote he moved was one of sincere and heartv gratitude and it was carried with prolonged applause. Dr Lotzy, in responding, made very effective, humorous u«e of the familiar story of the Scotchman who when his guest cried "Stop, stop !" was mean enough to stop.