i 



SIPHONALES 97 



down. The factors that determine the setection of the functional 

 nucleus from among the number available offer a problem for 

 future research. In the mature oogonium there is either a beak, the 

 apex of which gelatinizes, or else several pores through which the 

 antherozoids can enter the oogonium, fertilization taking place in 

 situ. 



The antheridia, which are usually stalked, commonly arise 

 close to the oogonia, though in V. sessilis they develop just prior to 

 oogonial formation. When the septum cutting off the antheridium is 

 laid down the nuclei divide, and cytoplasm gathers around each 

 daughter nucleus. The mature antheridium may be colourless or 

 green, and it opens by one or more apertures near the apex, thus 

 providing a means of escape for the pear-shaped antherozoids 

 which bear two flagellae pointing in opposite directions. After 

 fertilization the zygote develops a thick wall and remains dormant 

 for some time before it germinates to give rise to a new filament. 

 The latest evidence shows that reduction of the chromosome 

 number takes place when the zygote germinates, thus indicating 

 that the adult plant is haploid. This character is somewhat ano- 

 malous when contrasted with the diploid status of almost all the 

 other Siphonales, with the exception of the primitive Protosiphon. 

 This is yet another reason for suggesting that the true affinities of 

 Vaucheria are to be found with the Xanthophyceae. 



REFERENCES 



Caulerpa. ARwmssoN, T. (1930). Svensk hot. Tidskr. 24, 263. 



Caulerpa. Borgesen, F. (1907). K. danske vidensk. Selsk. Skr. 7, 340. 



Vaucheria. Couch, J. N. (1932-3). Bot. Gaz. 94, 272. 



Caulerpa. Dostal, R. (1929). Planta, 8, 84. 



Halimeda. Howe, M. A. (1907). Bull. Torrey Bot. Club, 34, 491. 



Neomeris. Howe, M. A. (1909). Bull. Torrey Bot. Club, 36, 75. 



Halicystis. Kornmann, P. (1938). Planta, 28, 464. 



C odium. Schmidt, O. C. (1923). Bibl. bot., Stuttgart, 91, i. 



Caulerpa. Schussnig, B. (1929). Ost. bot. Z. 78, i, 



Caulerpa. Schussnig, B. (1939). Bot. Notiser, p. 75. 



Phyllosiphon. Tobler, F. (1919). Jb. wiss. Bot. 58, i. 



Codium. Williams, M. (1925). Proc. Linn. Soc. N.S. Wales, 50, 98. 



CSA 



