200 Double Flotvers and Sex-Linkage m Begonia 



and not very rarely several of them may appear on the same plant. 

 Some of the more interesting of these forms will be spoken of later. 



An average of many i'^a families gives about 1 double in 32, but in 

 several large families no doubles at all appeared, and this average has 

 certainly no general significance. From F^ plants crossed back reci- 

 procally with various doubles, similar irregular numbers were obtained 

 and no approximation to analysis could be made. To render the com- 

 position of these families intelligible lengthy descriptions would be 

 required and little purpose would be served by the publication of such 

 details. Their interest lies chiefly in their value as an indication that 

 in regard to a character which in so many plants is distributed geneti- 

 cally according to strict allelomorphic rules, great irregularity may 

 elsewhere prevail. Whether this irregularity is in any way connected 

 with the monoecious structure of Begonias cannot of course be declared. 

 Such a conclusion is by no means improbable. 



The purpose of the present paper is to make known a curious dis- 

 covery which resulted when Begonia Davisii was brought into the series 

 of experiments. The plant is one originally found in Peru by Mr Davis, 

 collector for Messrs Veitch, and first flowered by them in the year 1876 \ 

 Inasmuch as this is a real species, breeding perfectly true on self- 

 fertilisation, it seemed suitable for use as a reliable single for crossing 

 with doubles. When however these crosses were made it was found 

 that any double fertilised by pollen of B. Davisii gives onli/ double- 

 flowered offspring — 405 plants have been thus raised, and of these only 

 18 are recorded as having less than complete doubling. The male 

 side of Davisii is therefore exclusively double-bearing. Since the 

 same plant fertilised with its own pollen gives only singles, the 

 female side must be inferred to be exclusively single. Tested however 

 with the pollen of a double, it gave a result which we cannot satis- 

 factorily interpret. Fertilisation with pollen of doubles cannot always 

 be accomplished, since thoroughly petalodic flowers do not produce 

 pollen. A good many doubles nevertheless when starved or poorly 

 grown do produce anthers and pollen, as for example the well-known 

 double called in horticulture Begonia Lloydii. B. Davisii $ fertilised 

 by Lloydii j' gave 72 thorough singles and 42 with traces of petalody, 

 a condition we have not yet seen in Davisii itself The genetic nature 

 of these slightly petalodic plants is not clear. If they can be formed 

 when the pollen of Lloydii is used, we should expect them to appear 

 when Davisii is fertilised with its own pollen, for this pollen used on 

 ^ See Wynne, The Tuberous Begonia, 1888, p. 10 and Bot. Mag., t. 6252. 



