THE PLANT WORLD 183 



Our Teachers' Department. 



Edited by Professor Francis E. LLtOyd, 



Teachers College, Columbia University, New York City. 



POLLINATION IN THE PRIMROSE. 



In an article entitled ' ' Observations on the Pollination of the Prim- 

 rose," * Dr. F. E. Weiss reexamines, in the light of observations made 

 by him in the spring of 1903, the question of the means of pollination 

 and the significance of heterostylism in the English primrose. His 

 general conclusions are that the flowers of this plant are both close- 

 and cross-pollinated efficiently. It was held by Darwin, and has been 

 generally accepted as true, that the seed of close-pollinated flowers produce 

 weaker offspring than those of cross-pollinated, and this point Darwin 

 sought to prove experimentally, with results which have not been contro- 

 verted, although they have been brought into question by field observers. 

 According to Weiss, the primrose flower is at first upright, but is later 

 horizontal or pendent. Exposed as the plants are to the action of strong 

 winds, it is easy to believe that the short-styled flowers would as a result 

 of the shaking by the wind be close-pollinated while in the vertical posi- 

 tion and similarly the long-styled form while in the horizontal. In the 

 cowslip, the opposite behavior is noted. In both, however, so far as the 

 mechanical facts are concerned, these may be interpreted as well for 

 close-pollination as for cross-pollination. It remains, therefore, to deter- 

 mine whether, in nature, the one method preponderates over the other, 

 and concerning this there is as yet no general agreement. That this is 

 true is attributable to only one cause, namely, that as yet a sufficient 

 number of exact observations have still to be made. The observations 

 of Weiss indicate the value of quantitative methods and the importance 

 that further study should lay greater emphasis upon this method. 



Weiss examined regularly each day, between 11 A. m. and 1 p. m., two 

 large patches of primroses. During eight occasions he observed the 

 flowers to be visited by about fifty insects. Two visits to two other 

 stations yielded fourteen insects exclusive of numerous small butterflies 

 (^Andrewas) . Of all these the most constant visitor is a long-tongued fly 

 (^Bomby litis), which pollinates the flower in the manner familiar to all. 

 Certain bumble-bees behave similarly, and other bees, however, are not 

 at all regular or efficient in pollination, while the Andrewas are to be 

 compared in general effectiveness to the fly Bombylius. 



There is obviously a considerable discrepancy between the number of 

 insect visitors reported by Weiss and the great number of flowers, though 

 the chances for cross-pollination even under these conditions would be 



* The New Phytologist, 2 : 99, April and May, 1903. 



