OCR Text |
Show 174 SPECULARIA SPECULUM. CHAP. v. - No. of Pot. TABLE LXVI. Lactuca sativa. Crossed Plants. - - - Inches. I. 27 First generation, 25 planted in open ground. -- II. 29~ Second generation, 17 ~ planted in open 12 g ground. - - III. 14 Second generation, 10~ kept in the pot. Total in inches. 136 Self-fertilised Plants. Inches. 2q 20 24 10 11 - -- - - 94 g 0 96 h . l:lt of the seven crossed plants is 19. 43, and The average mg . h 100 to 82 that of the six self-fertilised plants 16 1nc es; or as . XXI. CAMP ANULACEJE.-SPECULARIA SPECULUM. . In the closely allied genus, Ca mpanu1 a , in whli ch Sp. edcu tlhaeniar . l d d the anthers shed at an ear y peno walsl forme~l~h~~c a~h:;es to the collecting hairs which surro~ndl po en, an th t 'thout some mechamca the pistil beneath the stigma.; . so a Wl. ce I covered up aid the flowers cannot be ferti~1sed. d~~~ ::s;:o~ ~roduce a single a plant of Campanula carpatlnca, an 1 1 d l ts seeded pro- capsule, wb1'1 st th e surro unding uncovert e Pa· n of Specularia fusely. On the other hand, the presen splemes ed up as appears to set almos t as rna ny. capsules ..w len cfo v.e ra s I h'a ve when left to the visits of the Dlptera, which, as a: I did not seen, are the only insects that frequent the flowers. eousl selfascertain whether the naturally crossed andbsponftanseeds ~ut a. fertilised capsu1 e s con t a m· e d an equal num e£r ot ·1· d ' f' lowers, comparison of artificially crossed and self- er I Ise * It has long been known that another species of the genus, Specularia perfoliata, produces 11 perfect eleisto(Yene as we as . o•· flowerso and tu1. e .c ·mer arc L !OI course ~elf-fertile. CHAP. v. SPECULARIA SPECULUM. 175 showed that the former were p1'obably the most productive. It appears that this plant is capable of producing a large number of self-fertilised capsules owing to the petals closing at night, as well as during cold weather. In the act of closing, the margins of the petals become refiexed, and their inwardly projecting midribs then pass between the clefts of the stigma, and in doing so push the pollen from the outside of the pistil on to the stigmatic surfaces.* Twenty :flowers wel'e fertilised by me with their own pollen, but owing to the bad season, only six capsules wel'e produced; they contained on an average 21·7 seeds, with a maximum of forty-eight in one. Fourteen :flowers were crossed with pollt:n from another plant, and these produced twelve capsules, containing on an average 30 seeds, with a maximum in one of fiftyseven seeds; so that the crossed seeds we1·e to the self-fertilised from an equal number of capsules as 100 to 72. The former were also heavier than an equal number of self-fertilised seeds, in the ratio of 100 to 86. Thus, whether we judge by the numbel' of capsules produced from an equal number of flowers, or by the average number of the contained seeds, or the maximum numbel' in any one capsule, or by their weight, crossing does great good in comparison with self-fertilisation. The two lots of seeds were TABLE LXVII. Spec1.duria speculum. No. of Pot. Talle t Crossed Plant Tal11'St Self-fertilised in each Pot. Plant in each Pot. - Inches. Inches. I. II. III. IV. Total in inches. I * Mr. Meehan has lately shown (' Proc. Acad. Nat. Sc. l'hiladelphia,' May 16, 1876, p. 84) that the closing of the flowers of Clay..._ 18 15~ 17 19 22k 18 20 23 77•13 75•75 ionia virginica and Ranunculus bu?bosus during the night causes their self-fertilisation. |