560 PROCEEDINGS OF THE ACADEMY OF [1895. 



cations are directly due to external factors over which the plant 

 has no control. I am aware that the principle of natural selection 

 may find its application in the most subtle cases ; at the same time 

 it requires, in this particular instance, a considerable strain to make 

 it fit. In reference to dichogamy Mr. Meehan says positively that 

 the difference between the time of maturity of stamen and pistil is 

 caused by varying degrees of temperature and that dichogamy has 

 its origin in this circumstance, "that whatever its significance, it 

 arises from no effort innate to the plant itself, but from an outside 

 force that can have but little interest in cross-fertilization." 4 It is 

 peculiarly characteristic of the present day to seek for the effect of 

 external conditions and to experiment with the modifications that can 

 be brought about by changing these. For example, Prof. Goebel says 

 in reference to cleistogamic flowers, " We do not yet know the condi- 

 tions necessary for the production of cleistogamic flowers, but it may 

 be assumed even now that this production is influenced by external 

 factors wherever a plant has the power to produce such flowers." 5 He 

 then cites experiments made with ImpaMens fulva, where cleistogamic 

 flowers are the result of poor nutrition. Accordingly, it appears at 

 least possible that experiments might give similar results in reference 

 to dichogamy. 



Attention has often been called to the fact that in plants espe- 

 cially adapted to insure cross-fertilization, there exists in almost 

 every case a possibility of self-fertilization. The above statements 

 in regard to dichogamy, if of any value, point to a different con- 

 clusion concerning the final or at least possible autogamy from that 

 which is generally accepted. It is assumed that the flower is so 

 constructed that there is every chance of a cross, provided the insect 

 appears to do the work. This failing, the arrangement is such as 

 to allow pollen to come in contact with the stigma of the same flower. 

 It is evident that in every case which seems to point towards cross- 

 fertilization it is always to a great extent a matter of chance 

 whether the visitor arrives or not, even when the adaptation seems 

 most perfect. It should be decided if cross-fertilization or autogamy 

 is the rule with every species which seems constructed so as to 

 attract insects, and this work should be done in as many different 



4 Proc. Acad. Nat. Sci. Phila., Nov. 27th. 1888, p. 394. 



5 Goebel, Pflanzen-biologische Sohilderungen. Marburg. 1893, II Theil, 2 

 Lief., p. 363. 



