CROSSINGS IN MELANIUM-VIOLETS 



255 



Claiskn (1921) records such a segregating line. 

 The percentage of spontaneous crossings will 

 be very easy to determine by employing the me- 

 thod used in my experiments with beans (1921). 



The cause of the great constancy in V. tri- 

 color depends probably on the fact that this 

 species is pollinated by thrips. which live in 

 the flowers, and not by larger insects flying 

 from flower to flower. Wittrock has found 

 that this species is relatively rare visited by 

 larger insects; on the other hand, thrij)s are as 

 a rule present in the flower as well as in the 

 stigmatic chamber. Already Bennet has stated 

 the opinion that the pollination in V. tricolor 

 is largely performed by thrips. 



In order to study the behaviour of crosses 

 between autogamous and herkogamous types 

 of pollination one cross between V. arvensis 

 and V. tricolor was studied, viz. 2 X 10. The 

 former was autogamous and the latter was 

 herkogamous, i. g. self-fertile when pollinated 

 artificially with its own pollen, although un- 

 able, for reasons of construction of the flower, 

 to become self-pollinated when isolated with 

 parchment bags. 



The reciprocal Fi-hybrids resembled each 

 other. When isolated they did not give any 

 seeds. Thus herkogamy was shown to be a 

 dominant character. As to the characters of 

 the construction of the flower table 1 sum- 

 marizes the results. 



However, the dominance of herkogamy in 

 Fl is not a rule without any exception. In 

 one case, viz. the cross between V. tricolor am- 

 motropha (line 40), which is herkogamous, 

 and an arvensis-form (line 3). which is auto- 

 gamous, the Fi-generation becomes autoga- 

 mous. The pollen-magazine of line 40 (fig. 

 2B), however, is not quite closed, and this 

 may be the cause of the autogamy in Fi. 



'W 



