86 JouENAL OF THE MiTCHELL SociETY \_Septembei' 



The device was driven by a small water motor. In other respects 

 the conditions were the same as in the experiments previously de- 

 scribed. The results are shown in Table No. 11. From the 8 cul- 

 tures 40 male, 33 female, and 776 tetrasporic plants were obtained. 

 The 40 males and 33 females, representing a little more than 8% of 

 the entire growth, are not too numerous, it is thought, to be accounted 

 for as intruders, since the cultures were located in the midst of fruit- 

 ing plants. This experiment, therefore, fairly conclusively demon- 

 strates that only tetrasporic plants are produced by fertilized eggs. 



TARTHENOGENESIS 



As has been said above, it was noticed early in this work that un- 

 fertilized eggs germinated freely. It was assumed that these young- 

 plants would grow to maturity, but what they would produce was in 

 doubt. From the uncertainty in the writings of algologists as to 

 whether or not the sperms in the Dictyotaceae (4) are functional, it 

 was of course permissable to expect tetrasporic plants. On the other 

 hand, since it has been shown in the preceding experiments that 

 tetraspores invariably produce males and females, and that fertilized 

 eggs produce tetrasporic plants, as well as from analogy with other 

 algae (7), it must be assumed that the chromosome number is reduced 

 in spore formation and hence female plants and eggs must of neces- 

 sity contain the haploid number. It is difficult to see how the diploid 

 number characteristic of the tetrasporic plant (7) could be restored. 

 The writer inclines to the view already expressed that the sex of the 

 gametophytes is determined in the reduction division of the spore- 

 mother-cell. Therefore it would be logical for germinating unfer- 

 tilized eggs if they mature at all to produce female plants. 



These alternative views will now be discussed in connection with 

 the experiments. In 1912, 4 series of 4 shells each (see Table 3) 

 were carried through. Although they were all covered with germi- 

 nating eggs when planted, only 3 gave mature plants w^hen collected. 

 The cultures derived from female plants without males were strung 

 on the same wire with those from tetrasporic plants as well as with 

 those from both male and female plants, all on the same support. 



