474 SMITH 



ured the sex organs now known as antheridia and oogonia. Among other algae, 

 although not realizing its significance, he described and figured successive 

 steps of conjugation in species of "Conjugata" now referred to Spirogyra and 

 Zygnema. He was more fortunate than many present-day teachers of botany 

 in that he saw germination of the zygote of Spirogyra. . 



The erroneous ideas of Vaucher and contemporary students of reproductive 

 structure of algae rests in part upon their interpretation of them in terms of 

 floral structure. For example, Vaucher refers to the reproductive structures 

 of "Ectosperma" as anther and as seed. Another curious erroneous idea arose 

 shortly after discovery of motile reproductive cells of algae. It was thought 

 that formation of swarmers by algae was really a metamorphosis of certain 

 cells into "infusoria" (protozoa) which eventually metamorphosed back to 

 plant cells. Proponents of this idea held to it as late as 1850. 



A start toward proper understanding of the nature of reproductive bodies of 

 algae came with Agardh's (1836) abandonment of the floral terms used for 

 them and when he began calling reproductive cells spores instead of seeds. 

 He was not the first to use the term "spore" since it had been used before 

 in connection with mosses. Agardh distinguished between motile and non- 

 motile spores but did not give them special names. The term zoospore, now 

 so widely used, was coined by Decaisne (1842) but applied indiscriminately 

 to both sexual and asexual swarmers. An important distinction was made by 

 Pringsheim (1855) when he distinguished between sexual and asexual swarm- 

 ers. He restricted the term zoospore to asexual swarmers. 



It was through study of reproduction in algae that botanists' ideas con- 

 cerning the essential features of sexual reproduction were clarified. Long 

 before the middle of the last century botanists were aware of the necessity 

 of pollination for the formation of embryos of seed plants. By the middle of 

 that century there had been a demonstration that a pollen grain forms a 

 pollen tube which grows to the egg cell in the embryo sac of an ovule. There 

 then arose the following controversy: does the tip of the pollen tube grow 

 into the embryo, or does something passing from the tip of the pollen tube 

 (either a liquid or a discrete body) stimulate the egg cell to develop into 

 the embryo? This controversy was settled by discoveries made in algae. 

 Here it was shown for the first time that the essential feature in sexual repro- 

 duction is the fusion of male and female elements. In 1854 Thuret showed that 

 antherozoids are attracted to the "octospores" (eggs) of Fucus and that there 

 is no development of an egg into an embryo unless antherozoids and egg come 

 together. Thuret did not see the actual fusion of antherozoid and egg but 

 inferred that this took place. Thuret's inference was confirmed the next year 

 by Pringsheim (1855) when he reported for Oedogonium that an antherozoid 

 first comes in contact with an egg and then fuses with it. Demonstration of the 

 fusion of antherozoid and egg in Oedogonium and Vaucheria led De Bary 

 (1858) to interpret conjugation in Spirogyra and allied genera as essentially 



