SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 28l 



with various cultivated plants. Different types of crucifers 

 kohl-rabi, borccoli, Brussels sprouts, cabbage were grown near 

 each other and the seed resulting from pollination at will, when 

 grown, showed a large amount of intercrossing. The observation 

 was also made with different varieties of the radish, Raphanus 

 sativus. These plants are all partially self-sterile so that cross- 

 fertilization is expected in somewhat greater degree than would 

 result from random pollination. Mixing was also shown by 

 plants which are generally self-fertile such as tulip, hyacinth, 

 anemone, ranunculus, strawberry, orange, rhododendron, rub- 

 barb. The fact that vicinism occurs when varieties of these 

 plants are grown together is established by such observations 

 but this does not prove that one type of pollen is prepotent over 

 the other. Somewhat more significant results were obtained 

 from two other species. Mimulus luteus was found to be highly 

 fertile when insects were excluded. Uncastrated flowers of a 

 constant whitish variety were artificially pollinated by a yellowish 

 variety and of the 28 resulting plants all had yellowish flowers 

 so that the "pollen of the yellow variety completely over- 

 whelmed that from the mother plant." A crimson variety of 

 Iberis umbellate, which was self-fertile, was crossed with a pink 

 variety, the pollen being applied to uncastrated flowers as before 

 upon the stigmas of which he saw abundant pollen presumably 

 from the same flowers. Out of 30 plants raised 24 showed 

 themselves to be crossed by the altered color of their flowers. 

 Obviously experiments such as these are not sufficient to 

 establish the prepotency of foreign pollen in self-fertile plants. 

 A number of conclusions might be drawn from such results. 

 The cross-fertilized seeds may have germinated better and the 

 plants grown from them survived in greater numbers. The 

 types may not have been as constant for their flower color as 

 Darwin supposed or the ovules may not have been receptive 

 at the time the plant's own pollen was available but were when 

 the foreign pollen was applied. Taken as they stand the results 

 do indicate a prepotency of pollen from dissimilar plants and 

 it would be desirable to investigate this effect with these species 

 using mixed pollen in reciprocal applications as employed with 

 maize and the tomato. 



