168 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Zanardinia. Reinke (1877, 1878) found that in this genus the swarmers from the 

 plurilocular organs (of which there are two kinds — some with large and some 

 with small locules — both borne on the same plant) are gametes which con- 

 jugate in pairs, the smaller zooids functioning as male gametes. This was the 

 first observation of the actual fusion of gametes in brown algae. Eeinke noted 

 that in Zanardinia the unilocular sporangia occurred on separate plants and 

 found that the swarmers from these sporangia always germinated directly. In 

 view of the occurrence of an alternation of generations in higher cryptogams (as 

 had become well established by this time through the pioneering studies of Hof- 

 meister and others), Reinke had no hesitation in interpreting his observations 

 as indicating the occurrence in Zanardinia of a similar alternation between 

 gametophytic and sporophytic generations. 



This, then, is the first brown alga which was considered as showing this phe- 

 nomenon. At first botanists hesitated to accept Reinke's interpretation but its 

 accuracy was established cytologically by Yamanouchi (1911, 1913). 



Reinke (1878) and Falkenberg (1879) also observed the fusion of the zooids 

 from the plurilocular organs of Cutleria, a genus closely related to Zanardinia. 

 Both of them were of the opinion that another alga known as AgJaozonia (which 

 bears only unilocular organs) represented the sporophytic generation of Cut- 

 leria. The evidence in favor of this view accumulated in the course of the next 

 few decades and finally Yamanouchi (1909b, 1912) furnished cytological proof 

 of it. 



Berthold (1881b) studying the classical Ectocarpus siliculosus at Naples 

 found that also in this genus the zooids from the plurilocular organs were 

 gametes. He also saw the fusion of the gamete nuclei, an observation which had 

 been made only once before in plants — by Schmitz (1879c) in Spirogyra. Ber- 

 thold was unable to determine the role of the unilocular sporangia of Ectocarpus 

 since none of the plants obtained in the sea at Naples bore any. 



In consequence of the observations of Reinke, Falkenberg, and Berthold re- 

 garding the gametic role of the zooids from the plurilocular organs of Zanar- 

 dinia, Cutleria, and Ectocarpus a firm conviction developed among botanists 

 (and was adhered to for almost half a century) that the plurilocular organs of 

 brown algae were always gametangia and the unilocular organs sporangia. Not 

 infrequently it was found (e.g., by Berthold, 1881b; Sauvageau, 1896a, 1896b, 

 1897; Oltmanns, 1899; Kuckuck, 1891) that the zooids from the plurilocular 

 organs did not conjugate but germinated directly. To explain this asexual be- 

 havior the theory was usually advanced that the gametes had lost their sexual 

 power and germinated parthenogenetically. 



That this explanation was incorrect was shown by Knight (1923, 1929). Study- 

 ing Pylaiella (a genus related to Ectocarpus) and Ectocarpus, she demonstrated 

 that brown algae had two kinds of plurilocular organs: some occurring on hap- 

 loid plants and functioning as gametangia and some on diploid plants and func- 

 tioning as zoosporangia. The diploid plants frequently also formed unilocular 

 sporangia. Meiosis occurred in the unilocular sporangia, as had previously also 

 been shown by Yamanouchi with reference to Zanardinia and Cutleria and by 

 Kylin (1918) with reference to Chorda. No reduction divisions occurred in the 

 plurilocular sporangia of diploid plants and the zooids produced in them ger- 

 minated directly. 



