.144 Sex Characters in Beffonias 



the p;ut 111 phiiils Lo iindcrgu fertilization by means of insect instead of 

 wind agency, in association with the great evohition of insect life which 

 occurred in cretaceous and precretaceous times, the essential factor 

 which determined this adaptive change along primarily' female rather 

 than primarily male lines was probably, not any superior capacity for 

 fertilization so obtained (though this may have been a point in its favour), 

 but the greater facility afforded by the central position of the gynoecium 

 on the floral axis in providing for the longer retention of the embryo 

 in contact with the tissues of the parent plant. 



This growing tendency to retain the embryo in contact with the 

 mother plant, and thus provide it with a better start in the world, forms 

 a striking feature of plant development in recent times, just as the 

 tendency to retain the embryo in contact with the maternal tissues is a 

 marked characteristic of the mammalia, the highest order of animals. 



The ultimate aim, if one may be allowed the teleological expression, 

 has been the production of the largest number of offspring with the best 

 chances of successful separate existence, along with the greatest economy 

 of material, and the chief steps towards this end have been: — (1) The 

 replacing of the naked ovule by the ovule enclosed in an ovary, i.e. the 

 evolution of the Angiosperms. (2) The provision of nourishment in an 

 available form to as late a stage as possible in the growth of the embryo, 

 and this was secured by placing the ovary in the centre of the floral 

 axis. 



The provision for the passing of the jirothallus or asexual repro- 

 ductive stage while the embryo remains in contact with the maternal 

 tissues is also in harmony with this scheme. 



The ultimate test of the respective value of the unisexual as against 

 the hermaphrodite type of flower, is capacity to ensure, not merely the 

 fertilization of a large number of ovules but the survival of a large 

 number of embryos, and the central position of the gynoecium in the 

 hermaphrodite flower favours such survival. 



In this connection one is reminded of Baur's conception of hybrids 

 as Clinal and Periclinal Chimaeras. It is possible to apply this con- 

 ception to the hermaphrodite flower which would then be a sex-chimaera 

 built up on a clinal or central female basis with periclinal male accessory 

 organs. 



The problem of the central position of the gynoecium in the her- 

 maphrodite flower when I'educed to cytological terms becomes a question 



1 "Primarily" iu the sense described above in reference to the position of tlie 

 gynoecium. 



