PRO-EMBKYO OF CHARA. 



359 



of which the tissue of the future sporogonium is formed, and the more 

 deeply-placed cell gives rise to the tissue of the seta and foot (embryo- 

 phore). In Biccia, however, the whole oosphere is devoted to the for- 

 mation of the sporogonium. In Chara, the more superficial of the two 

 cells gives rise to the " pro-embryo " by repeated divisions, whereas 

 it appears that the deeply-placed larger cell undergoes no change. 

 Since their mode of origin is the same, it is reasonable to suggest that 

 the " pro-embryo " of Chara is the homologue of the sx)orogonium of 

 the HejKitica, and that the basal cell of the former is the homologue 

 of the seta and foot of the latter, — that the " pro-embryo " and the 

 basal cell together are equivalent to the sporogonium with its seta 

 and foot. It must not be forgotten, however, that in Chara the 

 " primary root " is derived from the apical cell as well as the 

 *' pro-embryo." From the researches of Nordstedt and Wahlstedt "^^ 

 it appears that this development of a "primary-root" is not 

 absolutely constant, and that when it does not take place the 

 whole of the apical cell gives origin to the "pro-embryo." This 

 fact affords some ground for regarding this root not as a " primary " 

 root, in the strict sense of the term, but rather as an adventitious 

 root. As I have endeavoured to establish elsewhere,! a " ])Yiia?ii'j 

 root " is an organ developed from that segment of the oosphere 

 which is diagonally opposite to that one in which the apex of the 

 stem is formed. Of this the Ferns and EquisetacerE and also the 

 Phanerogams offer good examples. When, as in Chara, the first 

 root is formed from that half of the oosphere which gives rise also 

 to the stem, it must be regarded as being adventitious. Of this 

 Selaginella and the ConifercB afford examples. It may be objected 

 that the inequahty of the two cells in Chara destroys the homology 

 which is here suggested, but this objection has not much weight. 

 It is not denied that the sporogonium of Pdccia is homologous with 

 the sporogonium, seta, and foot of one of the other HejMticte, 

 because in Fdccia the sporogonium is formed from the whole 

 instead of fi'om half of the oosphere, and therefore the homology of 

 the "pro-embryo" of Chara with the sporogonium of one of the 

 Hepatica, cannot be denied on the ground that it is formed from 

 a small part of an oosphere the greater part of which is devoted 

 to the formation of a foot. 



On this view the " pro -embryo," or rather the true " embryo " 

 of Chara must be regarded as the sporophore of the plant. The 

 following table will illustrate this view in all its consequences : — 



* Loc. cit. 



t On the Homologies of the Suspen; 

 January, 1878. 



Quart. Journ. Micr. Sci, 



