April 25, 1895J 



NATURE 



607 



writer conjectures it to be a iiybrid between lanata and populi- 

 'olia, var. leucanthus. 



If any one will look at the plates to which I have referred, 

 he may satisfy himself of the astonishing diversity of these 

 forms. In GarJ. Ma^. 1839, p. 430, is an early record of the 

 appearance of the new seedlings at shows. At the Caledonian 

 Horticultural Show, the Cinerarias " were very brilliant, and 

 partook of novelty." The names of the seedlings successful, 

 including -jiaterhoiisiana, are given. At the beginning of the 

 forties the named kinds became very numerous, and were at 

 first offered at high prices in the trade advertisements. Hen- 

 derson and Ivery were the two chief English cultivators at that 

 time. 



During this period, 1830-1840, the progress was very rapid, 

 and there can be no doubt that the florists' Cinerarias came into 

 existence within some ten or twelve years. Such a plate as that 

 in Jour, d'harl. Gand, 1846, shows the ordinary kinds much 

 as we know them. Froni those plants up to the perfected plants 

 of ten years ago, the change was undoubtedly slow and gradual. 

 The alterations have consisted chiefly in incre.ise in size and 

 symmetry of the flower, and in promotion of compactness of 

 habit (see, e.g., Glenny, Ann. of Hort. 1850, p. 37, also Card. 

 Chron. 1S79 (i), p. 532). 



The next point is of some interest. As compared with other 

 " improved " herbaceous plants, the Ciner.iria is a little peculiar 

 in the fact that it is now generally raised from seed. This is 

 done partly to ensure that the plants shall not be overgrown, 

 and partly to avoid green fly, a pest to which these plants are 

 specially liable. In consequence of this, the old " named" 

 kinds, that is to say, kinds propagated by ase.\ual methods, 

 went out of fashion, though till lately they still had supporters. 

 It was found that seeds of good strains could be fairly relied on 

 — not, of course, to reproduce the form of their particular parents, 

 but to give fine plants. For instance, Henderson, Scot. GarJ. 

 i. 1852, p. 22, says : "in raising seedlings you should select 

 three or four dwarf varieties, which number is quite sufficient to 

 produce all the different colours." In Card. Chron. 1887(1), 

 p. 549, are some interesting particulars of the methods used by 

 Mr. James, to whom the later improvement of the plant in 

 Kngland is largely due. The plants of each colour are grouped 

 in blocks, and the bees are freely admitted to the houses. It is 

 not found necessary to separate the plants further, and in saving 

 seed all the colours are mixed together. In ihe case of the 

 Cineraria therefore, as in that of Calceolaria-, Begonias, and 

 other plants much grown from seed, it is desirable not only to 

 create a fine variety of which the stock can at once be multi- 

 plied asexually, but also to raise a good strain of which the 

 seedlings come fairly true. The latter process may undoubtedly 

 often take time. 



Even in recent times a "sport" has been recorded. In 

 Card. Chron. 1880 (i), p. 277, it is stated that Mr. James 

 " has succeeded in obtaining a new ' break ' that promises to 

 be the forerunner of another host of new flowers. The colours 

 (if the flower do not shade off into one another, as is usually the 

 case, but are arranged in bold and well-defined belts. . . . We 

 understand that it flowered for the first time last season, and 

 that it has reproduced itself from seed." A figure is given. 



To these particulars might be added many more, relating to 

 the origin of double vaiieties, variations in the foliage, and other 

 matters. The foregoing notes of the history must, I think be 

 taken to show (i) that the modern Cinerarias arose as hybrids 

 derived from several very distinct species ; (2) that the hybrid 

 seedlings were from the first highly variable ; (3) that "sports " 

 f an extreme kind appeared after hybridisation in the early 

 years of the "improvement" of these plants; (4) that the 

 subsequent perfection of the form, size and habit has proceeded 

 by a slow process of selection. Mr. Dyer's statement that the 

 modern Cinerarias have been evolved from the wild C. criienia 

 "by the gradual accumulation of small variations " is therefore, 

 in my judgment, misleading, for this statement neglects two 

 chief factors in the evolution of the Cineraria, namely, hybridisa- 

 tion and subsequent " sporting." 



I have ventured to deal with this case because it seems to be 

 generally supposed by those not .acquainted with the facts, that 

 the origin of the modern florists' flowers has in general been 

 very gradual. As a matter of fact it would, I believe, be more 

 true to say that the new departures have in general been at 

 first very rapid, subsequent improvement being commonly slow. 

 "Sporting," usually after hybridisation, has been the chief 

 factor in the production of these new developments, just as in 



VO. 1330, VOL. 51] 



the case of the Cineraria. To speak of no more, I may refer 

 to the new forms of Begonia, of Gladiolus, and of Erica now 

 so familiar. With what special propriety the Cineraria was 

 chosen by Mr. Dyer to support his contention is not evident 

 to me. 



Whether any of these sports exhibit the phenomenon of organic 

 stability I cannot now discuss. W. Bateson. 



St. John's College, Cambridge, April 17. 



The Age of the Earth. 



In Dr. Hobson's letter on this subject, he confuses the argu- 

 ment by the introduction of a new factor (never alluded to in 

 the formerdiscus5ion,or in my theory as stated in "Island Life"), 

 the bulk or volume of the matter deposited. This has nothing 

 whatever to do with the practical problem, because it is 

 admittedly impossible to form<j»y estimate of the total bulk of 

 all the stratified rocks of the earth during all geological time ; 

 while it i> equally impossible to form any estimate of the total 

 bulk of the denuded matter, since we have no clue whatever to 

 the number of times the same areas have been again and again 

 denuded. But the maximum thickness of the same rocks, 

 compared with the average rate of denudation, and the co- 

 incident maximum rate of deposition, do furnish materials for 

 an estimate, since they can all be approximately determined 

 from actual observation ; and the result is what I have given. If 

 Dr. Hobson had referred to Ihe former discussion he would have 

 avoided imputing to me "fallacies " which I never made. I never 

 Slid a word about " equal bulks " of material being deposited in 

 less time than they were denuded. But, as the only available 

 data are those of thickness, not bulk, then it is clear that, if the 

 area of deposition is one-nineteenth of Ihe area of denudation, Ihe 

 rale of deposition of a known thickness of rocks will be nineteen 

 times as great as the known rate of denudation. It was neces- 

 sary for me to point this out when first discussing the subject, 

 because one eminent writer had made the rate of deposition less 

 than the rate of denudation, because the water-area is greater 

 than the land-area of the globe ; while an eminent geologist 

 has quite recently taken the rates of denudation and deposition 

 as being equal. If, however, the area of deposition is very 

 much /«i than the area of denudation, which is now admitted 

 to be the fact, then the rate of deposition per foot of thickness 

 will tie many times greater than the rale of denudation. 



I should not have thought it necessary again to state this very 

 obvious conclusion, had not Prof. SoUas, while so clearly point- 

 ing out Dr. Hobson's misconception as to the area over which 

 the maximum thickness of the strata extended, omitted to refer 

 to the confusion he has now for the first time introduced into 

 the problem, by references to the l>ulk or volume of the sedi- 

 mentary rocks, a factor which all previous writers have seen to 

 be wholly beyond even an approximate determination. 



Alfred R. Wallace. 



So little is really known about the earth's age that any addi- 

 tional mode of approximating toil, however rough, may possess 

 some value. The following method of finding a lower limit is, 

 with one or two alterations, the same as that given in a paper 

 in the Geological Magazine for 1887 (p. 348). It depends, not 

 on ihe rate of denudation, but on the rate of subsidence within 

 the area of sedimentation. 



Part of the sediment brought down by a river is used for 

 keeping the surface of the delta close to the level of the sea ; 

 and the fact that the deposits formed from it are generally shal- 

 low-water deposits, shows that the amount of sediment is, as a 

 rule, sufficient or more than sufficient for the purfwse. The 

 remainder of the sediment is carried out seawards, and enlarges 

 the delta laterally. 



If there were no surplus sediment, it is evident that the mean 

 rate of subsidence over the delta would be obtained by dividing 

 the volume of the sediment brought down annually by the 

 river by the area of the delta. But if there be an excess of 

 sediment, then the same quotient will give a value greater than 

 the mean rate of subsidence, for only part of the sediment is 

 used for keeping the delta-surface in shallow water. In the 

 case of the Mississippi, the amount of sediment brought down 

 annually is 7,459,267,200 cubic feet, and the area of Ihe delta 

 12,300 square miles, or 342,204,320,000 square feet ; so that 

 the mean rate of subsidence is not greater than ,',; of a foot per 

 year, or 218 feel per century. 



Prof. Sollas estimates the total maximum thickness of the 

 different layers of sediment since the beginning of Cambrian 



