282 



Pelrocelis Hennedyi and Crnoria pellita. Here also it must be presumed that the 

 tetrasporangia are formed without reduction of chromosomes. 



There are thus a considerable number of Cryptonemiales which difler with 

 regard to the course of development from the typical diplobiontic forms. 



SvEDELius'), referring to the simultaneous occurrence of monospores and te- 

 traspores in one and the same individual of Cliantransia efflorescens, considers it 

 not altogether impossible that future investigation of the cruciate tetrasporangia 

 may show them to have been produced without reduction of chromosomes. Up 

 to the present, however, no Floridea with such sporangia has been subjected to 

 closer cytological investigation. The Swedish writer points out in this connection, 

 that such sporangia are first divided by a transverse wall, and thereafter by two 

 perpendicular partitions, which he considers would hardly fit in with a reduction 

 division. It should nevertheless be borne in mind that we find, both in Arche- 

 goniates and in flowering plants, cruciate sporangia as well as zonate sporangia, 

 — though the latter, it is true, are more rare — and it seems not to be apparent 

 that the formation of a cell-wall on the first division would preclude the reduction 

 of chromosomes. As regards the zonate division, it has in several of the Coralli- 

 nacese been demonstrated with certainty that the three cell divisions take place 

 almost simultaneously, and that the nuclear divisions are completed before the cell- 

 division sets in (see p. 273). It is hardly likely that there should be any difference 

 in principle between the cruciate and the zonate division; among other reasons, 

 because we find both occurring in the species of the genus Hildenbrandia, — which 

 are doubtless very closely related — where the sporangia must also be presumed to 

 divide without reduction of chromosomes (cf. also Lithothamnion Sonderi, fig. 137). 

 If SvEDEi.n s' supposition were correct, it would involve either that the reduction 

 division must take place by the division of the zygote nucleus, in spite of the 

 presence of tetrasporangia, or that it never occurred among Cryptonemiales, since 

 the tetrasporangia, as far as we know, here never divide telrahedrically, but always 

 by parallel or cruciate walls, often markedly inclined. The latter alternative would 

 further imply that the cystocarpia were throughout developed by parthenogenesis, 

 which is not in accordance with the actual facts, as, though fertilization has not, 

 it is true, been cytologically demonstrated in any of these algae, which are furnished 

 with telraspores yet spermatia have at any rate been found attached to the 

 trichogynes in Dumontia incrassata (see above p. 158), Polyides rotundas (Thuret, 

 Et. phyc. PI. 38 figs. 14 — 18) and in certain Corallinacese {Choreonema Thuretii, Solms, 

 Corall. Taf. Ill, fig. 4, Corallina mediterranea, Solms, 1. c. Taf. Ill, fig. 19). 



On the other hand, it must be presumed that reduction division may also be 

 lacking in telrahedrically divided sporangia, as cases are also known where such 



') N. SVEDELIUS, 1. C. p. ."iO. 



') The fertilization lias Ijecn cytologically demonstrated in Gloiosiphonia capillaris by Oltmanns; 

 but this Alga has usually no tetrasporangia. 



