Xo.506] 



NOTES AND LITERATURE 



506 



order. Tetrasporie plants have 40 chromosomes in their nuclei. 

 This number is reduced by the first nuclear division in the tetra- 

 sporangium. During synapsis the 40 chromosomes become 

 grouped to form 20 pairs, which become exceptionally clear in the 

 stage of diakinesis. The first or heterotypic mitosis separates the 

 members of the pairs, thereby halving the number and giving 

 after the second mitosis 20 chromosomes to each of the tetra- 

 spores. Vegetative mitoses in the male and female plants show 

 uniformly 20 chromosomes and it must be assumed that these 

 sexual plants develop from tetraspores. The chromosomes are 

 organized in the prophases of mitosis directly from a chromatic 

 network and without the interpolation of a spirem stage. The 

 spcnnatntigia are cut off in pairs to the right and left of a mother 

 cell and in each spermatangium a uninucleate sperm is organized 

 (20 chromosomes) which on escaping leaves behind an empty 

 cyst. The young carpogonium is uninucleate but an early divi- 

 sion differentiates the female gamete nucleus (20 chromosomes) 

 which remains in the carpogonium. and a trichogyne nucleus that 

 shortly breaks down. The carpogonium terminates a 4-celled 

 carpogonial branch borne by a cell ("tragzelle") from which 

 develops also an auxiliary cell and certain sterile cells. The 

 sterile cells enlarge greatly after the fertilization of the carpo- 

 gonium and then break down, forming a mass of slime which 

 apparently serves to give space and protection for the develop- 

 ment of the gonimoblasts. In some way not clearly understood 

 the zygote nucleus of the fertilized carpogonium enters the auxil- 

 iary cell and from this cell as a starting point the gonimoblasts 

 arise as a dense growth of short filaments. The cells of the goni- 

 moblasts contain nuclei derived from that of the zygote and con- 

 sequently have 40 chromosomes which are passed on to the carpo- 

 spores developed in rows. From the carpospores must come the 

 tetrasporie plants with their 40 chromosomes. We have there- 

 fore in Dclesseria an antithetic alternation of generations exactly 

 parallel with that of Pohjsiphonia. a diploid phase including the 

 gonimoblasts and the tetrasporie plants alternating with a haploid 

 Phase represented by the sexual plants. 



Svedelius 8 opened a new vista in cytological studies on the red 

 algffi with his discovery of multinucleate tetraspore mother cells 

 »i Martensia, one of the Delesseriacea. The young cell has 

 8 Svedelius, N., "Ueber den Bau und die Entwicklung der Florideengat- 

 UDg Mart ensia," Kungl. Svensk. Vet.-akad. Handl, XLIII, No. 7, 1908. 



