582 SUMMARY OF CUERENT RESEARCHES KELATING TO 



done is to show that in that complete and well-defined unity, the 

 Floridefe, there exist two quite different types of reduction-division ; 

 and this explains the fact that some genera are wholly devoid of 

 tetraspores, which are, as a rule, so characteristic of the group. The 

 non-tetraspore-bearing Floridete (Nemalionales) have a reduction- 

 division, which immediately follows fertilization. The monospores 

 ■which occur in these types are pure germ-cells, which are not a necessary 

 link m the course of the alternation of generations. These two types of 

 reduction-division differ in this way, that in the first type only one kind 

 of individual occurs, namely (monoecious or dioecious) sexual individuals 

 with or without monospores ; while in the second type two kinds of 

 individuals occur, namely, partly sexual individuals, monoecious or 

 dioecious, and partly asexual tretraspore individuals ; and between these 

 two kinds of individuals there takes place a regular alternation. Since 

 the first type is characterized by the appearance of the plant in only one 

 form, it is here called haplobiontic ; the second type, which appears ni 

 two forms, is called diplobiontic. It must be noted that these different 

 forms in the diplobionts do not coincide strictly from the cytological 

 standpoint with the two generations, since the diploid gonimoblast and 

 the carpospores belong equally to the diploid sporophyte generation. 

 The form in this sense must therefore not be confused with the 

 generation. As to the problem concerning priority of type the author 

 shows that the haploid gametophyte is primary and the diploid secondary. 

 The probable original development of the diploid from the haploid is. 

 described. The diploid tetraspore-forming generation must have been 

 formed at one jump, so to speak, as is shown by the author. The 

 question as to what effect this discovery of the two types of reduction- 

 division will have on the systematic arrangement of the Floridefe is 

 propounded. It cannot be left out of consideration. 



Position of Chromatophores.*— G. Senn writes on the position of 

 the chromatophores in the palisade cells of marine Florides. In 

 Peyssonnelia Squamaria and Platoma cydocolpa the chromatophores, in 

 a diffused illumination of medium intensity, lie in antistrophe on the 

 portions of the membrane turned to the light. If the under side of the 

 thallus of Peyssonnelia is illuminated, the chromatophores are obliged 

 to collect in the anatomically lower cell-ends, which are then the best 

 lighted. By prolonged darkening of the cells of Platoma, apostrophe 

 can be caused ; intensive illumination, on the other hand, produces 

 parastrophe. The difference between the arrangement of the chroma- 

 tophores in the palisade cells of marine alga? (antistrophe) and of foliage 

 (epistrophe) under optimal diffuse illumination is due to the difference 

 of optical conditions. If water is injected into the intercellular air 

 spaces (which in leaves bring about the total reflection of the light rays 

 which have penetrated into the palisade cells) so as to make the optical 

 conditions equal to those of the marine alg«, then, under a convergence 

 of light rays of 90° and more, the same arrangement of chromatophores 

 takes place in the palisade cells of the leaves as in those of the FloridoB 

 examined, namely, antistrophe. 



* Act. Soc. Helvet. Sci. Nat., Session 97 (1915) p. 203. 



