THE HORTICULTURAL SOCIETY OF NEW YORK 



flower on that same plant as it is to carry such pollen to a flower 

 of another plant and the chances for doing so are greater. Adap- 

 tations which limit self-pollination do not necessarily restrict close- 

 pollination. In such cases the agent effecting close-pollination be- 

 comes an important factor in pollination, but the planting in solid 

 blocks of such a clonal variety does not complicate or limit the 

 possibility of the action of this agent. With the adequate opera- 

 tion of the insects, either a single plant of the Red Clover, or a solid 

 block planting with one clone of the Red Clover, or a planting with 

 every plant a different seedling would be pollinated equally well. 

 Without any action of insects there would be the same restriction 

 in fruit setting, provided, of course, that the factor deciding the 

 setting of fruit is solely that of pollination. 



But structural adaptations may advance in complexity until 

 close-pollination is also restricted. In certain Primulas, Lythrums, 

 and Orchids there are different forms of flowers for individuals 

 or for groups of plants. These are such that it is mechanically 

 easier for insects to effect certain "legitimate" cross-pollinations. 

 In such cases the exclusive growing of a clone having one form of 

 flower tends to reduce pollination. It appears, however, that such 

 a specialization does not exist to a marked degree in any of the 

 important fruit crops at least in those grown in temperate regions 

 or that have perfect flowers. 



What has just been said regarding structural adaptations for 

 cross-pollinations applies as well to those adaptations in which 

 the pistils and stamens in individual flowers mature at different 

 times (condition called dichogamy). In most plants, d'chogamy 

 prevents self-pollination but not close-pollination. Thus in the 

 single-flowered types of the garden Geraniums the stamens of a 

 flower shed pollen considerably in advance of the maturity of the 

 pistil of that flower. But there are usually flowers of various ages 

 after opening on the plant, so there is a chance for insecLs to carry 

 pollen from flower to flower on a plant or from plant to plant of 

 one clonal variety. There is, hence, a pollination problem and the 

 action of insects is necessary to effect pollination, but the growing 

 of a clonal variety does not make it the more difficult. In most 

 fruit crops, Apple, Pear, Peach, etc., there is a partial dichogamy, 



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