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Show 446 GENERAL RESULTS. CllAP. XII. It is obvious that the exposure of two sets of plants durjn.g several generations to different conc~itio~1s can lead to no beneficial results, as far as eros. 1ng 1s concerned unless their sexual elements are thus affected. ' . That every organism is acted on to a certan1 extent 1y a change in its environment, will not, I prcsn~11e, be . disputed. It is hardly necessary to advance ovlllcnce on this head ; we can porcoi ve the difference between individual plants of the sam species which have grown in somewhat more shady or sunny, dry or <lamp places. Plants w hieh have been propagated for some crenerations under dif£ rent cli1natos or at different ~easons of the year transmit different constitutjons to their seedlings. Under such circumstances, the cheInical constitution of their fluids and tho nature of their tissues are often modified.* Many other such facts could be adduced. In short, every alteration in tho function of a part is probably connected with some corresponding, though oft n quito imperceptible change in structure or composition. \iVhatever affects an organis1n in any way, likewise tends to act on its sexual el 1nents. W o see this in the inheritance of newly acquired modifications, such as those fro1n the increas c1 use or disuse of a part, and even fron1 mutilations if followed by disoaso.t We have abundant ovid nee how su ceptible tho reproductiv system is to changed conditions, in the 1nany instances of animals rendered sterile by confinement; so that they will not unite, or if they unite do not * Numerous cnses together with re~ ronces arc giv(m in my' Variation under D0mostication,' ch. xxiii. 2nd edit. vol. ii. p. 26!. With roHpcct to animal , Mr. Brackcnriclge has w 11 shown ('A Contribution to the Theory of DiathC'sis,' Edinburgh, lSGD) tlmt the different orgnns of animals arc oxcite<l into different dcg,rces ofnctivity by differon<'C. of temperature ami rood, and become to a certain xtont adnptc>d to th o~ . t 'Variation unclcr ~omcstwn.~ tion,' ch. xii. 2nd od1t. vol. 1. p. 4(36, CHAP. XII. . GENERAL RESULT'. 447 produce offspring, though the con:finom nt m b 1! f 1 ,, ay 1ar rom c ose; anu of plants renuered ste ··l b l . va t I· on. B u t hardly any cases a.IY' ,,, n e. y c. u . ti- 'd . c uoru more stnklnO' evi ence how powerfully a chan o·e l·n th a· . b 1'£ c o e con Itlons of 1. e actsf on the sexual elements than th l· d 1 ' ose a rea y grven, o p ants which are completely self-sterile in o. ne hc ountry, and wh. en brou(o) 'ht to anoth . . ld ..-~ er, yie ' even In t e first generation, a fair supply of self-fertiliseu seeds. But it Inay be said, granting that changed conditions act on the sexual elomen ts how can t • ' \-YO or more plants gro.wing close together, either in their native country or In a garden, be differently acted on, inasinuch as t~e.y appear to be exposed to exactly the same cond'dit ionds ? . Although this question has been al· d rea y cons1 ere , It deserves further consideration u d l . n er nse v· era points of view. In my experiments 'th ·t z· WI ~g~ a ~~ _PUrpurea, some flowers on a wild plant were self-fertilised, and others were crossed with pollen f~om another plant growi~g within two or three feet's distance. The crossed and self-fertilised plants raised ~rom the seeds thus obtained, produced flower-stems In number as 100 to 47, and in average height as 100 to 70.. Therefore ~he cross between these two plants was highly beneficial; but how could their sexual e~ements have been differentiated by exposure to d1fferent conditions ? If the progenitors of the two plants had lived on the same spot during the last score of generations, and had never been crossed with any plant beyond the distance of a few feet in all probability their offspring would have been reduced to the same state as some of the plants in my experiments, ~such as the intercrossed plants of the ninth generat~ on of Ipomooa,-or the self-fertilised plants of the eighth generation of Mimulus,-or the offspring from |