78 



NATURE 



[November 28, 1907 



from time to lime iiulcpcndcnlly, but always, I thiiil-c, in 

 cultivated ground. There is a tendency in maples to 

 revert to a ternary symmetry, as is shown by the occasional 

 production of three carpels instead of two. The sycamore 

 often produces seedlings with three cotyledons. I grew 

 some of these, and they had for a time leaves in whorls 

 of threes, but soon reverted to pairs. I have only 

 heard of one case of an adult wild maple with leaves 

 three in a whorl. 



There are some singular mutations which occur in the 

 broad-leaved trees of temperate countries, but probably 

 always under somewhat artificial conditions. They seem 

 10 be merely correlated with habit, and are quite indepen- 

 dent of affinity. The normal angles at which the branches 

 are set on either become very acute or very obtuse ; in the 

 one case we get pyramidal forms like the Lombardy 

 poplar, in the other weeping forms. Or the cell-sap is 

 deeply coloured red, masking the green of the chlorophyll 

 corpuscles (copper-beech). In other cases the leaves lose 

 their normal circumscription, and are deeply divided (fern- 

 leaved beech). Apparently all these mutations are in some 

 degree perpetuated by seed, but they do not hold their 

 own in nature, and owe their preservation to planting in 

 gardens and elsewhere. It is not easy to speculate as to 

 the cause of these singular mutations. One may infer 

 from the fact that they are related to habit, and not to 

 aflinity, that they are not due to reversion. 



While specific stability under constant conditions appears 

 to be the rule in nature, it is widely different in cultiva- 

 tion. When a plant is brought under cultural conditions 

 it maintains its type for some time unaltered, then gives 

 way and becomes practically plastic. From my experi- 

 ence at Kew, where I saw the process continually going 

 on, I hazarded the generalisation that any species, annually 

 reproduced from seed, could be broken down in about five 

 years. During that period specific stability, though 

 menaced, tends to maintain itself. Darwin was well aware 

 of this, and as for the moment his books seem to be little 

 studied, I will quote the passage : — 



" We have good grounds for believing that the influence 

 of changed conditions accumulates, so that no effect is 

 produced on a species until it has been exposed during 

 several generations to continual cultivation or domestic- 

 ation. Universal experience shows us that when new 

 flowers are first introduced into our gardens they do not 

 vary ; but ultimately all, with the rarest exceptions, vary 

 to a greater or less extent" ("Animals and Plants," ii., 

 p. 261). 



He quotes in support the testimony of well-known 

 experts. Thus Salter, the great raiser of chrysanthemums, 

 states : — " Everyone knows that the chief difficulty is in 

 breaking through the original colour and form of the 

 species." Vilmorin, the most distinguished French horti- 

 culturist of his time, maintained that " the first step is 

 to get the plant to vary in any manner whatever ; for the 

 fixed character of the species being once broken, the desired 

 variation will sooner or later appear." 



.Abundant illustrations of the fact which has been stated 

 are furnished by the history of individual species. Thus 

 Sabine says of the first dahlia plants introduced into 

 Europe : — " At Madrid they were a long time in the Royal 

 Garden without any indications of change." The history 

 of the Zinnia and of the .Swan River daisy is the same. 

 A few years ago Mr. Watson, the curator of Kew, gave 

 me notes of cases which had come under his own observ- 

 ation. Primula japonica w.as introduced in 1871 as " a 

 new crimson primrose." In 1877 it produced rose- 

 coloured as well as various shades of magenta flowers. 

 Aiilfiuriiiin scheraerianum, introduced in 1862, had in 1874 

 produced enormously developed spathes, and in 18S0 a 

 form with two spathes to each spadix. In 1874 it was 

 crossed with a white variety, and that called rothschild- 

 iaiiiim, with mottled spathes, was the result. It is interest- 

 ing to note that " the seedlings are nearly all mottled like 

 the parent." Impaliois Siiltani was introduced at Kew 

 from Zanzibar in 18S1. For several years it did not vary. 

 It now exhibits half-a-dozen distinct shades of red in the 

 flowers. The fine Cape orchid, Disa grandiflora, has long 

 been in cultivation in this country ; varieties were unknown 

 until it was raised from seed bv Dr. Moore at Glasnevin. 



I may add two cases which have more particularly come 

 under my own notice. Nemesia struinosa, a rather local 

 South African plant, was introduced about 1892. It now 

 shows indications of breaking up into two distinct races, 

 with the greatest variety in the coloration of the 

 flowers. 



The most remarkable, however, is that of Primula 

 obconica, introduced in 1882. For many years it was per- 

 fectly stable, but within the last few has exhibited the 

 most surprising variation both in the number, form, and 

 colour of the flowers. 



In all these cases I think we may safely infer from 

 the persistent specific stability at the commencement of 

 cultivation that the changes which subsequently occur 

 would not have occurred in nature. We cannot regard 

 the one state as in any way a continuation of the other. 

 The changes which occur under cultural conditions are, in 

 fact, something sui generis. We may say, of course, if 

 we lil\e, that the potentiality of such changes was latent 

 in the species in nature ; but, as a matter of fact, if so, it 

 was suppressed, and there is no evidence of its being 

 called into activity. 



The evidence, on the other hand, that such changes 

 follow cultural conditions as a result is simply overwhelm- 

 ing, and I do not suppose that Mr. Lock denies it to be 

 the case. The only question can be as to how they 

 operate. Now there is one point in connection with plants 

 under cultivation the importance of which I have not 

 seen referred to. It is this : in nature we deal with a 

 host of individuals ; in cultivation with a very limited 

 number. In my view specific stability is maintained 

 partly by the weeding out of unfavourable variations, 

 partly by wide interbreeding. Now it is obvious that 

 under cultivation the latter agency is inoperative, and 

 cultural conditions bring other influences to bear, especially 

 as regards nutrition ; but these I have no space to 

 discuss. 



I take it that the species in nature has two weapons in 

 reserve for self-preservation. Of these, variation is the 

 most effective if given time, as it will act automatically. 

 Mutation, on the other hand, though it might now and 

 again hit the mark, is likely in most cases to overshoot 

 it, and is therefore seldom called into play or utilised ; and 

 observation seems to confirm this. 



In the development of a plant under cultivation the 

 horticulturist takes advantage of both variation and muta- 

 tion. In the case of the Cyclamen, I have shown that 

 the fine forms now existing are almost entirely the result 

 of accumulated variation. As with the garden Cineraria 

 there has been mutation in floral coloration : but the small 

 amount of variation in the foliage proves. I think con- 

 clusively, that in other respects the latter has gradually 

 been evolved from the wild Cineraria criictita, though 

 Darwin, from second-hand information with which I 

 supplied him, stated otherwise. 



The case of the Chinese primrose is extremely interest- 

 ing. When introduced in 1820 it had probably already 

 undergone some cultural development at the hands of the 

 Chinese. It was slowly developed in Europe for a long 

 period without manifesting any striking structural change, 

 until it bore little superficial resemblance to the wild 

 stock. This was discovered in the gorge of the Yangtse, 

 and when introduced into this country proved very intract- 

 able of cultivation ; in fact, I doubt if at the moment it 

 is to be found in our gardens. Within about the last 

 quarter of a century the cultivated form has exhibited 

 two very remarkable mutations, and it is interesting to 

 observe that these appear to recur independently. The 

 first was the so-called " fern-leaved form." I do not know 

 if this was ever fixed, but, if so, it did not take the public 

 taste, and W'as not preserved ; but fern-leaved individuals 

 appear to occur casually in batches of seedlings of quite 

 distinct races with the ordinary foliage. The transition 

 from the palmatifid to the pinnatifid form of leaf is theo- 

 retically interesting. Nothing can well look more different 

 than a fan-palm and a feather-palm, but we can see an 

 intermediate stage in an Australian Livistona. The second 

 mutation, the " ivy-leaved form," is much rarer, and in 

 everv way more remarkable. Tt is apparently accompanied 

 bv more or less floral abortion, and it has not been found 



NO. 1987, VOL, yy] 



