Self-fertilization

At this stage of my enquiry 1 can draw only a few tentative conclusions from the case-histories presented above. I shall return at the end of the book to the issue of how disciplines evolve and when, to adopt biological parlance, a new discipline becomes self-fertile. 

Selbstandigkeit, /. Independence, self-reliance. Selbst-ansteckung, /. self-infection, -befruch-tung, /. self-fertilization, -beherrschtmg, /. self-control, -bestaubuog, /. (Bot.) self pollination. 

Flowers must be pollinated for fruit to form (see alsop.290). Some apples are "self-fertile"— pollination is achieved by bees flying from flower to flower on the same tree. Others cannot set a crop on their own and need to be planted within bee-flying distance of another cultivar that is both compatible and in flower at the same time. Your neighbors yard is usually close enough. A crab apple can also make an effective pollinator. 

See facing page if you are buying a single tree, check with the supplier that it is a self-fertile cultivar if buying two or more, ensure that they are compatible. 

Although most varieties are self-fertile, they benefit from hand-pollination, moving from flower to flower, dusting lightly with a soft paintbrush on a warm, dry day when flowers are fully open. Do this several times over two weeks, as flowers open in sequence. 

A very common evolutionary route in plant speciation is the evolution of self-fertilizing species from outcrossing progenitors (Stebbins, 1970 Wyatt, 1988). An increase in self-fertility in mine ecotypes was demonstrated for both A. capillaris and Anthoxanthum odoratum by McNeilly and Antonovics (1968), and for Armeria maritima by Lefebvre (1970), though there is no evidence that mine plants in the wild self-fertilize more than normal plants of these species. There are a variety of selective forces leading to the evolution of self-fertility (Jain, 1976), but in this context the most likely cause is the need for reproductive assurance in a marginal habitat. 

Many species of plants reproduce, in part, by self-fertilization, and, therefore, Equation 1 apply only to individuals that result from crossfertilization. The inbreeding which results from self-fertilization can be defined by the parameter F, the decrease in the frequency of heterozygotes (1), and Equation 1 becomes... 

Such a population will approach equilibrium where F = (1 — a)/(l + ) (2). The parameter a defines the binomial frequency for cross-fertilization, and (1 — a) defines the frequency for self-fertilization. The population can now be described in terms of its reproductive mode (3)—viz.,... 

Consequently, the more highly self-fertilizing the population, the larger are the dispersive effects of genetic drift. 

Stebbins, G. L., Self-Fertilization and Population Variability in the Higher... 

Pears, like apples, are as a rule not self-fertile. Good pollination is therefore very important. Observations have shown that Conference, for example, gives better-shaped fruit when Doyenne du Comice is present as the pollinator. Table 3.10 gives a rough guide to possible pollinators. Certainly there are a number of other cultivars which could be considered as potential pollinators, e.g. Comtesse de Paris, but most of them are difficult to market. 

Partly self-fertile shape of fruit. flowers later, but good... 

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