1895.] NATURAL SCIKNCES OF PHILADELPHIA. 561 



localities and at different times of the year as possible, since there is 

 no doubt there are great variations possible in the fertilization of 

 flowers in the same species caused by different conditions of heat, 

 moisture, etc. 



If autogamy should in any case prove the rule we must regard 

 fertilization by aid of an insect as an exception, not to call it an 

 accident, Dichogamy probably is then in a measure due to exter- 

 nal conditions. If this is true it is simply the result of a " lagging 

 behind'' in the ripening time of either stamens or pistils, and the 

 final autogamy is the result of a subsequent " catching-up " in this 

 respect. This is, as I have said before, probably the most interest- 

 ing side of the question, and the one which will no doubt prove the 

 most satisfactory for experimental investigation. 



In conclusion I desire to make the following suggestions: — 



First: — It is evident that the study of the phenomenon of cross- 

 fertilization of flowers by means of insects is still a profitable field 

 for observation and discovery. 



Second: — The effect of external conditions in reference to dich- 

 ogamy should be the subject of critical experiments. 



Third: — Teleological explanations should be avoided as much 

 as possible, here as elsewhere, according to the spirit of modern in- 

 vestigation. 



Finally: — The relative number of cases of cross- and close-fertiliza- 

 tion should be compared, and it should be determined if cross-fertiliz- 

 ation actually takes place in all cases where this is assumed. 



