STUDIES ON THE PLANT CELL. VIL 



BRADLEY MOORE DAVIS. 



SECTION V. CELL ACTIVITIES AT CRITICAL PERIODS OF 

 ONTOGENY IN PLANTS (Continued}. 



5. APOGAMY. 



APOGAMY is the suppression of the sexual act and the devel- 

 opment of a succeeding generation asexually. The term was 

 first proposed by De Bary in 1878, following Farlow's ('74) 

 discovery of the phenomenon in Pteris cretica. The succeeding 

 generation may arise in one of two ways : ( i ) by the develop- 

 ment of an unfertilized egg or gamete which is termed partheno- 

 genesis, or (2) by some form of vegetative outgrowth from the 

 sexual plant, a process which has been called vegetative apogamy. 

 We shall not attempt to give a detailed account of apogamy in 

 the plant kingdom but will confine ourselves chiefly to the con- 

 sideration of a few detailed studies of recent months which have 

 taken up the cell problems concerned. The cell problems nat- 

 urally treat of the processes which may be substituted for the 

 sexual act in ontogeny and the fundamental problems of the 

 behavior of the chromosomes under these conditions. 



Parthenogenesis has been known for many years among the 

 thallophytes which furnish illustrations in a variety of groups. 

 In the algae we have the well known examples of Chara crinita, 

 Cutlaria, Dictyota, some species of Spirogyra and Zygnema, and 

 a number of types in the lower Chlorophyceae and Phasophycese 

 whose motile gametes will germinate like zoospores should they 

 fail to conjugate with one another. The recent studies of Wil- 

 liams (:04b) on Dictyota give the only observations which have 

 been made on nuclear activities during the parthenogenetic 

 development of eggs in any algal form and will be considered 

 presently. The fungi furnish beautiful illustrations of partheno- 



