Functions of the Perianth. 9 



words on the functions of the individual parts, and on 

 the advantages presented by certain conformations of 

 the perianth, the androecium, and the gynsecium. 



The main functions of the androecium and gynsecium 

 are sufficiently well known. And how essential it is, 

 that the generative cells in particular shall be per- 

 mitted to develop themselves without external disturb- 

 ance, scarcely needs mention. So also we may assume 

 it to be admitted, that one of the offices of the perianth, 

 at the time when the generative cells are being de- 

 veloped, is to protect the parts in which this develop- 

 ment occurs, that is to say, the androecium and gynsecium, 

 from external interference. At a later period it is also 

 certainly one of the most important offices of the 

 perianth to protect the coherent pollen, when discharged 

 from the anthers, against premature wetting by rain or 

 dew, against displacement by wind and by unbidden 

 guests, as also against the destructive attacks of sundry 

 animals. A still further and very frequent function of 

 the perianth is to bring about autogamy,'' in those cases, 

 that is, where the pollen from other flowers is not 

 brought into contact with the stigma. And a fourth 



^ I understand by autogamy the fecundation of a flower by the 

 pollen from the androecium of the same flower ; by geitouogamy, 

 the fecundation of a flower by pollen from other flowers on the 

 same plant ; by xenogamy, the fecundation of a flower by pollen 

 from other plants. Geitonogamy and xenogamy may be classed 

 together under the name allogamy. Such terms as " self-fer- 

 tilisatiou " are to be avoided on account of their excessive iudefi- 

 niteness. 



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