1895.] NATURAL SCIENCES OF PHILADELPHIA. 557 



no species is altogether cleistogamous, taken as a premise, the follow- 

 ing conclusion is drawn: "Thus, cleistogamy, with all its special ad- 

 vantage, testifies to the value of intercrossing." The same hias, 

 looking favorably upon cross-fertilization, may be observed in most 

 writers on the subject. The prevailing impression seems to be that 

 close fertilization is, as a rule, only resorted to when all the chances 

 for cross-fertilization are at an end. 



It appears that the problem permits of a wholly different solution. 

 Among the few writers who admit this, there is perhaps none who 

 speaks with as much decision and who adduces as many facts to 

 prove his assertions as does Mr. Meehan. In his interesting paper, 

 entitled "Are Insects any Material Aid to Plants in Fertilization" — 

 the conclusions are as follows : — 



First : The great bulk of colored flowering plants are self- 

 fertilizers. 



Secondly : Only to a limited extent do insects aid fertilization. 



Thirdly : Self-fertilizers are every way as healthy and vigorous, 

 and immensely more productive than those dependent on insect aid. 



Fourthly: That where plants are so dependent, they are the worse 

 fitted to engage in the struggle for life, the great underlying principle 

 in natural selection. 



These views are directly opposed to the impression one would natu- 

 rally receive from text-books on botany. It is evident that it is of 

 the utmost importance to study the significance and, if possible, the 

 cause of each of the various factors with which we have to deal as 

 pointing either towards cross- or towards close-fertilization. As 

 already suggested, it is always a critical matter to generalize where 

 thousands of species are concerned which have developed under a 

 variety of circumstances. 



Let us now consider the chief adaptations which point towards 

 cross-fertilization : — 



I. Distinct sexes. 



II. Specially adapted or conspicuous corolla. 



III. Peculiar position of stamens and pistils. 



IV. Difference in the time of maturity of stamens and pistils. 



I. Distinct sexes. The male and female flowers being separated 

 it is a matter of necessity that the pollen of one flower finds its way 

 to the stigma of another flower. From a teleological point of view 



