84 G. F. PAPENFUSS 



has not only extended immensely our knowledge of the life cycle 

 and development of a very remarkable group of organisms, but 

 it touches upon questions of fundamental importance to all bi- 

 ology. 



These investigators have succeeded in growmg representatives 

 of this order of tropical algae, especially species of Acetabularia, 

 in culture for several generations. (For methods of culture see 

 Hammerling, 1934.) Thus they have had available at all times 

 an abundance of material of known parentage and age, which 

 has enabled them to study a variety of problems under well-con- 

 trolled conditions. Of die many interesting facts that have been 

 learned, the following merit special mention. 



In contradiction to the long-standing belief that these plants 

 are multinucleate, it has been found that they are uninucleate, 

 with the possible exception of Cymopolia barbata (L.) Lamour. 

 (cf. Hammerling, 1944). The nucleus is large and lobed and is 

 located in one of the arms of the basal rhizoid. The plants are 

 diploid. When they become fertile, the primary nucleus divides 

 mitotically and the so-formed secondary, smaller nuclei migrate 

 up the axis and into the gametangia. Each of the operculate cysts 

 that are formed in the gametangia contains at first a single nu- 

 cleus. This nucleus next undergoes a series of mitotic divisions 

 and later all the nuclei divide meiotically. The swarmers that are 

 ultimately produced in the cysts are gametes. 



A particularly convenient feature of Acetabularia is that the 

 cysts, zygotes or sporelings will remain dormant or become so 

 if kept in darkness. It was found that zygotes of A. crenulata La- 

 mour. would still germinate after having been in darkness for 

 eight and one-half months, that the cysts would liberate gametes 

 after storage in darkness for as much as a year, and sporelings 

 that were two and one-half months old remained alive in dark- 

 ness for as long as eight and one-half months. Another very ad- 

 vantageous feature is that the mature cysts can be induced to lib- 

 erate their gametes by a short treatment with distilled water. It 

 is of great interest that in culture the plants fail to become calci- 

 fied. The reason for this is still unknown but it immensely 

 facilitated the cytological and experimental work. 



