281 



haploid, and the diploid phase is restricted to the undivided zygote cell. To these 

 Florideae belongs, among the species mentioned in the present paper, Halarachnion 

 ligulatum. Gloiosiphonia capillaris must also be haplobiontic on the coasts of Den- 

 mark, where, as on those of France, tetrasporangia-bearing plants have never been 

 found, though they have been met with on the coasts of Norway and Sweden 

 (see p. 278). 



On the other hand, there are species which only propagate by tetraspores^ 

 not sexually. This applies first of all to the Hildenbrandia species, which are ex- 

 tremely common with tetraspores, but have never been found with sexual organs. 

 In Cruoriopsis gracilis also, and Rhododermis Georgii, sexual organs are quite unknown. 

 Rhododermis elegans again, has always been found with tetrasporangia only, save 

 for the case of some specimens from North-east Greenland, which bore antheridia. 

 There are moreover some Corallinaceaj which have hitherto been found in Danish 

 waters only with tetrasporangia [Litholhamnion Iccve, glaciale, Sonderi, norvegicum, 

 and Icevigatum). In all these, at any rate those first named, tetraspore formation 

 must be supposed to take place without reduction of the chromosomes. 



It should further be noted that in some species, albeit possessing both kinds 

 of spores, the two kinds do not occur with like frequency. This is probably the 

 case with several of the Litholhamnion species just referred to, the sexual plants 

 being presumably not altogether lacking, but merely rarer than those bearing tetra- 

 spores, and have therefore not hitherto been found. On the other hand, sexed 

 plants of Polijides rotundas seem to be far more common than the tetraspore plants 

 in the Danish waters. All this might seem to suggest that these species have no 

 regular alternation of generations, such as takes place in the typical diplobiontic 

 Floridese, in which sexual plants and those bearing tetraspores are nearly alike in 

 point of frequency. 



Parthenogenesis has been shown with certainty in Platoma Bairdii by Kuckuck. 

 In the Little Belt, it appeared in the same manner as at Helgoland, the antheridia 

 lacking, whereas cystocarpia and tetrasporangia were found. Here also the tetra- 

 sporangia must be formed without reduction of the chromosomes. Possibly partheno- 

 genesis may also occur in other Cryptonemiales. Some observations would seem 

 to suggest that this may be the case in Furcellaria fasligiata. The fact that I did 

 not find the spermatia attached to the trichogynes I do not consider as of great 

 importance; more significant, however, is the finding of an unfertilised carpogonium 

 with a short trichogyne, but which had nevertheless formed an outgrowth which 

 could only be regarded as a sporogenous filament (cf. p. 169, fig. 85 D). — In Petro- 

 celis Hennedyi I found, in some instances, sporogenous filaments growing out from 

 carpogonia which showed no interruption of the plasmatic connection with the 

 trichogyne (fig. 98 E, 99 E) and here also, no spermatia were found attached to the 

 trichogynes. 



Finally, some cases have been noted where tetraspores and sexual organs 

 appeared in one and the same individual. This has occasionally been found in 



D. K. D. Videiisk, Selsk. Ski-., 7. R:L'kke, nalurviilensk. o(,' matheni. AfiL VII. 2. 36 



