356 THE "pro-embryo" of chara. 



The interpretation given by Pringsheim" of the facts discovered 

 by him is to this effect : — He considers that the structure which 

 springs from the oospore of Chara, and to which he gives the name 

 of " pro-embryo " (Vorkeim), is the exact morphological equivalent 

 of the protonema which is developed from the spore of a Moss, and 

 he infers from the existence in these plants of leafless structures 

 intervening between the spore and the leafy plant, that the 

 Charace(T and the Muscinem are closely allied. This close relation- 

 ship is, he believes, placed beyond doubt by the fact that Mosses 

 alone of all plants possess organs which are analogous to the '* pro- 

 embryonic branches " (Zweigvorkeime) of Chara. The researches of 

 Schimpert shew that " rhizoid prothallia" occiu- on the stem and 

 leaves of many Mosses. 



In proceeding to inquire into the adequacy of this interpretation, 

 it may be at once admitted that the Characea resemble the 

 Muscinea;, in many points. Pringsheim does not fail to note in his 

 above-mentioned work the similarity in structure and development 

 existing between the nucule of Chara and the archegonium of a 

 Moss. It is usual at the present time I to place the Characea in the 

 class Carpospore(B, and to speak of the nucule as a carpogonium. 

 The soundness of such a classification becomes questionable when 

 it is remembered that both in structure and development, as well 

 as in the changes which it undergoes in consequence of fertilisation, 

 the nucule of Chara differs absolutely from a typical carpogonium. 

 The central cell (oosphere) of the nucule is surrounded fi'om the 

 first by a multicellular investment, and consequently that formation 

 of a cystocarp around the oos^jhere after its fertilisation, which is 

 so characteristic of the Carposporecr., does not take place in the 

 Characece. It is i^robably more correct to speak of the nucule of the 

 CharacecB as being an archegonium. 



In a recent paper upon the alternation of generations among the 

 Thallophytes, § Pringsheim groups the Characea with the Fucacea 

 and the Conjiif/ata;, as being plants which do not present that 

 dimorphism of the organs of fructification which is essential to the 

 occurrence of alternation of generations. In making this state- 

 ment he becomes unconsciously illogical. If, as he insists in his 

 first paper, the " jiro-embryo " of Chara be homologous with the 

 protonema of a Moss, and if, as he asserts in his second paper, 

 there be no stage m the life-history of Chara w^hich corresponds to 

 to the asexual generation (sporophore ||) of the Moss, it must be 

 admitted that the product of a fertilised oosphere is morpho- 

 logically equivalent to the product of a germinating spore ; that, 

 for instance, the sporogonium of a Moss is equivalent to its pro- 



* Loc. cit. p. 318, quoting from ' Monatsber, d. Berl. Akad.', 18U2. 



} ' Recherches anat. et morpbol. sur les Mousses.' Strasbourg, 1818, pp. 

 13, 15, 10. 



J ' Sachs, Lehrbucb,' 4te Auflage, 1874. 



§ ' Jahrb. I'lir wiss. Bot.', Bd. xi. 1877, p. 32. 



II Thiselton Dyer has suggested the word " oophore " as a general expression 

 for the sexual and " sporophore " for the asexual generation of plants. These 

 terras are used in this sense throughout this paper. 



