510 



[Vol. L 



Svedelius 15 gives a cytological study of Scinaia furcellata 



tion of the eystocarp in those red algae which lack the tetrasporic 

 phase in their life histories. Monosporangia and spermataii-ria 

 occur on the same plants growing out of and becoming cut off 

 from mother cells at the surface of the thallus with evidence that 

 successive crops may be formed from the same mother cells. 

 Both monosporangium and spermatangium have a nucleus with 

 about 10 chromosomes and the similarity of their structure and 

 manner of development indicates that they are homologous or- 

 gans. The 3-celled carpogonial branch requires a somewhat de- 

 tailed account since its history presents phases not previously de- 

 scribed for the red alga?. The terminal cell becomes the carpogo- 

 nium and a mitosis gives a nucleus to the trichogyne as has been 

 described for Batrachosprrmum, X< malum, Polysiphonia, Rhodo- 

 mela, Delesseria and Griffithsia. From the second or hypo-mums 

 cell is formed a group of 4 auxiliary cells rich in protoplasmic 

 contents. The third or basal cell of the carpogonial branch de- 

 velops finally the envelope of the eystocarp. The nuclei of the 

 carpogonial branch including the female gamete nucleus in the 

 carpogonium have 10 chromosomes which is the haploid number 

 of the Scinaia plant. After the fertilization of the carpogonium 

 the zygote nucleus, with 20 chromosomes, and consequently 

 diploid, passes into one of the auxiliary cells which have become 

 more or less fused together. In the auxiliary cell the large zygote 

 nucleus prepares for and passes through a heterotypic mitosis 

 with apparently clear evidence of diakinesis shown in the presence 

 of 10 pairs of chromosomes. A second mitosis gives the tetrad of 4 

 nuclei but only one of these becomes concerned with the develop- 

 ment of the gonimoblasts, passing back into the carpogonium 

 from which the gonimoblasts arise. The other 3 homologous 

 nuclei of the tetrad together with the nuclei of the auxiliary cells 

 take no further part in the history of the eystocarp. Nuclei of 

 the gonimoblasts have 10 chromosomes and this number is passed 

 to the carpospores which are formed successively in rows ; some 

 of the gonimoblasts remain sterile and develop into long fila- 

 ments resembling paraphyses. 



A most unexpected outlook upon the life histories of the red 

 alga? will be opened if these conclusions of Svedelius on Scinaia 

 are confirmed and if studios on X< ntalion, fiaf radios per mum, etc., 



"Svedelius, N., < « Zytologisch-Entwieklungsgeschicbtliche Studien tiber 

 Scinaia furcellata," Nov. Act. Beg. Soc. Scien. Upsal, IV, No. 4, 1915. 



