858 



THE " PRO-EMBRYO OF CHARA. 



This statement of the case makes it evident at a glance that the 

 hyi^othesis of the dii-ect conversion of the oosphere of Chara by- 

 fertilisation into a single carpospore results in a paradox. It 

 compels us to regard the carpospore of Chara as being not only 

 the sporophore but also the first stage of the oophore of the plant ; 

 or, in other words, to consider the carpospore of Chara as being 

 the morphological equivalent of the oospore of Coleochcete and of 

 the sporogonium of a Moss, and, at the same time, of a single 

 spore of either of these plants, a view which is quite untenable. 

 Moreover, such a direct conversion of an oosphere into a single 

 spore is quite unparalleled among plants which exhibit an alter- 

 nation of generations. In all such plants the result of the develop- 

 ment of the fertilised oosphere is the production of numerous 

 spores. Further, the mode of " germination " of this " carpospore " 

 of Chara is quite different fi-om that of the spores of other plants. 

 Wheu a l; :ore germinates it usually protrudes a germinal filament 

 (Keimschlauch) from any portion of its surface, but in Chara the 

 protrusion of the filament is confined to a definite spot, and its 

 formation is preceded by certain well-defined and apparently 

 constant cell-divisions. It appears, therefore, that this view of the 

 alternation of generations in Chara is unsatisfactory, for it is based 

 upon an unwarrantable assumption, and it fails to explain all the 

 phenomena of the life-history of the plant. 



An attempt may now be made to give an interpretation of these 

 phenomena which shaU have a more secm-e foundation, and which 

 shall interpret them in a more satisfactory manner. The first 

 ceU-divisions which take place in the fertilised oos^Dhere of Chara 

 are not unlike those which take place in that of ColeochMe, but the 

 final result is diflercnt in the two cases ; in ColeochcBte the cells 

 formed fall apart, but in Cliara they remain connected and certain 

 of them give rise to the " pro-embryo " and to the " primary root." 

 The processes of growth exhibited by the "germinating carpospore" 

 of ( hara corresj)ond much more nearly to those which accompany 

 the development of an embryo from a fertilised oosphere than to 

 those which occiu- in a germinating spore. It is interesting to 

 compare, from this point of view, the embryology of Chara with 

 that of the Hepatka. In Chara, the first division of the oosphere 

 takes place, as we have seen, in a plane at right angles to the long 

 axis of the archegonium, and this is the case also among the 

 higher Hepatica (Jungermannieaa) ; but this difference exists, that 

 in Chara two unequal cells are formed, whereas the two cells of the 

 Hepatica are equal in size. The more superficial of the two cells in 

 the Hepaticm — the one, that is, which immediately underlines the 

 neck of the archegonium — undergoes numerous divisions, by means 



