THE '* pro-embryo" OF CHARA. 357 



tonema — a result which is obviously incorrect. An attempt might 

 be made to escai)e from this dilemma by surrendering the sup- 

 posed homology of the " pro -embryo " with a protonema, main- 

 taining, however, the assertion that no alternation of generations 

 presents itself in the life-history of Chara ; but this would only 

 lead to further difficulties. Such a view would at once isolate 

 Chara from all other hving organisms as being an individual the 

 fertilised "ovum" of which produces an embryo quite unHke its 

 parent, from which the sexual individual is subsequently formed 

 by a process of budding. The life-history of Chara can be satis- 

 factorily accounted for only on the assumption that an alternation of 

 generations occurs in it. 



It is admitted by those who agree in placing the Characea 

 among the CarposporecB that an alternation of generations does exist 

 in the life-history of Chara, and the following is a brief account of 

 the supposed mode of its occurrences. To make it quite clear a 

 comparison may be instituted between Chara and a typically car- 

 posporous j)lant such as Coleochate. As the result of fertilisation, 

 the oosphere of Coleochxte undergoes successive divisions, which 

 give rise to a number of similar cells. This mass of cells, invested 

 by the walls of the mother-cell, is the sporophore of Coleochate, for, 

 at a later period, these cells become isolated ; each of them is in 

 fact a sj)ore (carpospore), and from each of them a zoospore is 

 emitted, fi'om which the oox3hore is developed. In Chara the 

 fertilised oosphere does not give rise even to so simple a spore- 

 producmg apparatus as that of ColeochcBte. It remains unicellular ; 

 it is, in fact, converted dnectly into a single carpospore, and this 

 is all that rej)resents the sporophore in the life-history of Chara. 

 It is only when this si3ore is about to germinate that it becomes 

 multicellular by the formation of cell-waUs within it in the manner 

 described by De Bary. This comparison may be conveniently 

 expressed in the following tabular form : — 



This view certainly harmonises with Pringsheim's theory of the 

 homology of the " pro-embryo " with a protonema, but it presents 

 obvious difficulties. It is not easy to realise that the so-called 

 carpospore of Chara is the morphological equivalent of the whole 

 oospore of Coleochmtc, and therefore also of so complex a structure 

 as the sporogonium of a Moss, and these difficulties are very much 

 increased by Pringsheim's recent paper above referred to. In it he 

 satisfactorily demonstrates that the spore of a Moss or of a Fern, 

 for instance, is not the final stage of the s^Dorophore, but that it is 

 the first stage of the oophore. This being the case, the table given 

 above is incomplete, all mention of the spore (except in the case 

 of Chara) being omitted. In its complete form it is as follows : — 



