320 



MICROSCOPIC FORMS OF VEGETABLE LIFE. 



cells pour their endochromes into a dilatation of the passage that 

 has been established between them; anditisthere that they com- 

 mingle, so as to form the spore or the embryo-cell. But in the 

 Zygnema (Fig. 108), which is among the commonest and best 

 known forms of Conjugatepe, the endochrome of one cell passes 

 over entirely into the cavity of the other; and it is within the 

 latter that the spore is formed (c), the two endochromes coa- 



FiG. 108. 



Various stages of the history oi Zygnema qurninum: — a, three cells, a, 6, c, of ii yoQiig filnmeiit, of 

 which 6 is undergoing subdivision ; b, two filaments in the first stage of conjugation, showing the 

 spiral disposition of their endochromes, and the protuberances from the conjugating cells ; c, com- 

 pletion of the act of conjugation, the endochromes of the cells of the filameiu a having entirely pa.ssett 

 over to those of filament b, in which the sporangia are formed. 



lescing into a single mass, around which a firm envelope gradu- 

 ally makes its appearance. Further, it may be generally observed, 

 that all the cells of one filament thus empty themselves, whilst 

 all the cells of the other filaments become the recipients ; here, 

 therefore, we seem to have a foreshadowing of the sexual dis- 

 tinction of the generative cells into " sperm-cells" and " germ- 

 cells," which we have just seen to exist in the Coufervaceae 

 (§ 198). And this transition will be still more complete, if (as 

 Itzigsohn has afiirmed) the endochrome of certain filaments of 

 Spirogyra breaks up before conjugation into little spherical 

 aggregations, which are gradually converted into nearly color- 

 less spiral filaments, having an active spontaneous motion, and 

 therefore corresponding precisely to the antherozoids of the truly 

 sexual Protophytes.' 



' This group of plants seems to serve as the connecting linlc between those simple 

 Protophytes in which the sexes are not yet tiifferentiated, and those higher fijrms in 

 whicli the distinction between the "sperm-cells" and " germ-cells" is very apparent. 

 For let it be supposed that in Sphceroplea (§ 198) a conjugation of two adjacent cells 

 were to take place, at that stage in their development in which the endochrome is 

 uniformly arranged in rings, no differentiation of sexes yet showing itself, — the process 

 wotild in all respects correspond with that of the ordinary Conjugateie. Again, whilst 

 in Mesocarpus, the two conjugating cells appear to take (as in the iJesmtrffffi, § 169) fi 

 precisely siiriilar share in the formation of their product, the first stage of differentiation 



