12 EXPERIMENTAL POLLINATION. 



and vaselin with the lowest possible melting-point and corresponding 

 penetration. The individuals must be marked and observed from day to 

 day, and only those utilized which are essentially normal. The tests 

 should be made under natural conditions with materials to which the insect 

 has been accustomed, and should meet the requirement laid down by 

 Forel, namely, that the insect recognize a certain substance and dis- 

 tinguish it from others in a constant and indubitable manner when normal 

 and not when mutilated. The application of such tests to normal insects, 

 those with the antennae coated and those with the olfactory pores cov- 

 ered, should be decisive. The results can be rendered even more decisive 

 by covering the insects' eyes and contrasting the response of insects with 

 either the antennae or the olfactory pores coated to fragrant flowers that 

 are habitually visited. Many other modifications of insects are possible 

 and can be developed as need arises, such as removing the scopa, attach- 

 ing artificial ones, filling the corbiculse with wax, etc. In connection with 

 determinations of efficiency, constancy, etc., it is helpful to stain the 

 pollen of various species with particular dyes and thus simplify reading 

 the pollen record of its behavior. One of the most interesting series of 

 experiments contemplated deals with the reversal of the characteristic 

 habits of diurnal and nocturnal pollinators. 



Life-history methods and records. — In the endeavor to determine the 

 exact relation of the flower and its behavior to the habitat, simple methods 

 have been devised for following and recording all changes in minute detail. 

 Quite apart from yielding a complete account of the development of the 

 flower, such records have proved indispensable in correlating floral changes 

 with physical factors and insect behavior, as well as in connection with 

 competition and autogamy. The methods are essentially observational, 

 though the subject affords an increasing opportunity for the use of experi- 

 ments in the correlation of flowers or parts. The essential features are: 

 (1) labeling flowers in the order of development; (2) visiting the plants 

 sufficiently often to obtain a detailed record; (3) recording changes on a 

 tabular form that permits ready checking against the preceding observation. 

 The usual plan has been to mark two or three adjacent plants and to follow 

 the development of 10 flowers on each simultaneously. This furnishes an 

 adequate check on individual behavior, and it is practically impossible to 

 follow a larger group when a number of species is concerned. When the 

 buds are sufficiently large, a label is attached to each and the flowers 

 are numbered in the order of their appearance. Ordinary price-tags are 

 employed and the size determined with respect to the flower. In the case 

 of minute flowers, especially those of umbellifers and grasses, the smallest 

 tags are too large for individual flowers, and other devices must be employed. 

 Tags may be placed at every third or fifth flower in large umbels or at 

 corresponding spikelets in panicled grasses, but in the smaller inflorescences 

 this often produces great distortion. Diagrams with the flowers numbered 

 sometimes afford the best solution, while with the smaller radiate heads 

 of composites the rays may be numbered in ink and thus furnish divisions 

 that enable one to follow the disk-flowers accurately. In large heads and 

 umbels and such spikes as those of Phleum, the inflorescence is labeled and 



