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THE AMERICAN NATURALIST [Vol.L 



like its neighbors several nuclei which by division increase in 

 number as the cell enlarges until about 50 are present. Then a 

 general nuclear degeneration sets in coincident with an increase 

 in the amount of cytoplasm and only one nucleus in the center of 

 the plasma mass survives to give rise to the 4 nuclei that enter 

 the tetraspores. A similar situation was found by Svedelius 9 in 

 Nitophyllum punctatum, a related form of the same family, which 

 is described in greater cytological detail. Typical mitoses in the 

 young tetraspore mother cell give it a dozen or more nuclei all 

 with about 40 chromosomes, the diploid number for the species. 

 Many of the nuclei shortly begin to show signs of degeneration 

 by the disappearance of the chromatin so that only the nucleolus 

 remains to take the stain, and there is also a shrinkage of the nu- 

 clear membrane. The degeneration is not simultaneous, a few 

 nuclei increase in size and give indications of preparation for the 

 heterotypic mitosis as shown by clear stages of diakinesis. How- 

 ever only one nucleus carries the history of reduction further and 

 thus becomes the surviving nucleus of the tetraspore mother cell, 

 a nucleus very much larger than the degenerating structures that 

 lie about it in the cytoplasm. At diakinesis pairs of chromosomes 

 are clearly shown, about 20 in number. The members of the pairs 

 are separated by the first mitosis which is therefore heterotypic 

 and a reduction division as in Polysiphonia, Griffithsia and 

 Delesseria. The second mitosis, homotypic, gives the four nuclei 

 of the tetraspores, each with about 20 chromosomes. It is very 

 interesting to note that the red algae present illustrations of 

 nuclear degeneration at a period of reproduction when it may 

 be desirable to conserve the cytoplasm of a cell for a limited num- 

 ber of reproductive elements. This nuclear degeneration appears 

 to be strictly analogous from a physiological point of view to 

 that exhibited in the oogonia of Vaucheria. Saprolegnia and 

 Albugo, in the sporangium of Derbesia, and in the oogonia of 

 certain forms of the Fucacece. 



With the cytological and experimental evidence in complete 

 accord and so strongly in favor of the theory of an antithetic 

 alternation of generations in those red alga? which have tetra- 

 sporic plants certain observations which at first thought appear 

 to offer exceptions to this theory naturally take on a high degree 

 of importance. The literature records a number of species which 



o Svedelius, N., "Ueber die Tetradenteilung in den vielkernigen Tetra- 

 sporangiumanlage bei Nitophyllum punctatum," Ber. deut. hot. Gesell, 

 XXXII, 48-57, 1914. 



