Leaf colour patterns, vegetative and sexual reproduction of Episcia ...

Results: The results are listed in table 3. The P/O ratio of Episcia lilacina is 36,34 : 1.
Table 3 Results concerning the P/O ratio.
Bud number
Number of pollen
grains
Number of ovules P/O
1 40120 1052 38,14
2 34528 1046 33,01
3 40560 1082 37,49
4 35080 956 36,70
5 35414 974 36,36
Average value 36,34 (±1,99)
Discussion: Pollen-ovule ratios are correlated with the breeding systems of plants (Cruden
1977). They reflect pollination efficiency, i.e. the likelihood of a pollen grain reaching a stigma
(Cruden and Miller-Ward 1981). Cruden (1977) divided the ratios of different plants into five
classes of reproductive systems: xenogamy (P/O about 5800:1), facultative xenogamy (about
800), facultative autogamy (about 170), obligate autogamy (about 30) and cleistogamy (about 5).
The evolutionary shift from class to class is accompanied by a significant decrease in the mean
P/O. The more efficient the transfer of pollen, the lower the P/O. That means for Episcia lilacina
that about 36 pollen grains come on one ovule. Due to Cruden (1977), this result would indicate
obligate autogamy. A much higher P/O ratio would be expected. Mistakes can of course not be
excluded entirely. But even if the result of the pollen grain count would be twice as high the next
class would be barely reached. The P/O ratio results of this work do not fit in the system of
Cruden because obligate autogamy of Episcia lilacina can be definitively excluded.
Examining the amount of pollen grains and ovules it is obvious that a lot of ovules (averagely
1022 ovules) were developed in one gynoecium. Comparing this fact with the high amount of
pollen grains the low P/O ratio seems to be more comprehensible. The numerical amount of
pollen grains and ovules were not further considered by Cruden (1977). This circumstance makes
comparisons between the results of Episcia lilacina and other plant families difficult.
Nevertheless, many different factors may influence the pollen-ovule ratio (Preston 1986), for
example:
• Enlargement of the stigma area; it can receive more pollen grains despite of a
constant pollen-transfer area on the pollinator (Cruden and Miller-Ward 1981).
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