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Show 268 SUMMARY OF MEASUREMENT·. CHAP. VII. fertilised plants of the fourth illcgitin1ato rrcnoration we:·e raised. The forn1or wore to the ] at tor i~ height as 100 to 46, and in f rtility during one year as 100 to 5, and as 100 to 0 • 5 clnrin o· tho next year. In this case, howev r, we have nob moans of distinguishing betw on the evil f~ .ts of illco·itimate fertilisation continued during four generations (that is, by pollen of the sa1ne fonn, but taken from a distinct 1lant) and strict self-fertilisation. But it is probable that these two processes do not differ so essentially as at ~rst appears to be ~l~e case. In tho following exp. enment any doubt ansing from illogitiinato fertilisation was completely elirnina ted. C!~·) Primula veris. (hqunl-styl d, rod-flowered vanety ).-Flowers on plants of th s concl self-fertilised ge~eration w re crossed with pollen frmn a distinct van ty or fresh stock:, and oth rs· wore arrain selffert~ l~sed. Cross d plants and plants of tho ~hird selffertihs~ d generation, all of lorritimato ori gin, were thus raised ; and t.h form r was to the latter in height as 100 to 85, and in fertility (as judged by the number of capsules produc d, together with the averao·e number of seeds) as 100 to 11. b Summary of the Measurem,ents in Table 0.--This table includes the heights and often the woio·hts of 292 plants derived from a cross with a froshb stock, an~ of 305 plants, either of self-fertilised origin, or derived from an intercross betw en plants of the same stock. These 597 plants belong to thirteen species and twelve genera. The various I rocantions which were taken to ensure a fair co1nparison have already been stated. If we now look down the rio·ht-hand l . b co l~I?n, In which the Incan height, weight, and fertihty of the plants derived from a eross with a fresh stock are represented. by 100, we shall see CHAP. VII. TABLE C • . 269 by the other figures how wonderfully superior they are both to the self-fertilised and to the intercrossecl plants of the same stock. With respect to height and weight, there are only two exceptions to the rule, nan1ely, with Eschscholtzia and Petunia, and the latter is probably no real exception. Nor do these two species. offer an exception in regard to fertility, for the plants derived from the cross with a fresh stock were much more f rtile than the self-fertilised plants. The difference between the two sets of plants in the table is generally much greater in fertility than in height or weight. On the other hand, with some of the species, as with Nicotiana, there was no difference in fertility between the two sets, although a great difference in height and weight. Considerino· all the . . b cases In this tal>le, there can be no doubt that plants profit immensely, though in different ways, by a cross with a fresh stock or with a distinct sub-variety. It cannot be maintained that tho benefit thus derived is due merely to the plants of the fresh stock being perfectly healthy, whilst those whieh had been long intercrossed or self-fertilised had become unhealthy; for in most cases there was no appen,rance of such unhealthiness, and we shall see under Table A that the intercrossed plants of the same stock are generally superior to a certain extent to the self-fertilised,- both lots having been subjected to exactly the same conditions and being equally healthy or unhealthy. vVe further learn fro1n 'rable C, that a cross between plants that have been self-fertilised during several successive generations and 1cept all the time under ~early uniform conditions, does not benefit the offspring In the least or only in a very slight degree. l\1imulus and the descendants of IpoinOJa named Hero offer instances of this rule. Again, plants self-fertilised |
