5 50 MICROSCOPIC FOKMS OF VEGETABLE LIFE THALLOPHYTES 



cells pour their endochromes into a dilatation of the passage that 

 has been established between them ; and it is there that they com- 

 mingle so as to form the zygospore. But in the various species of 

 Spiroyyra (fig. 420, B), which are among the commonest and best 

 known of Conjugate, the endochrome of one cell passes over entirely 

 into the cavity of the other ; and it is within the latter that the 

 zygospore is formed (C), the two endochromes coalescing into a 

 simple mass, around which a firm envelope gradually 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 filament become the recipients. Here, therefore, we'^seem 

 to have a foreshadowing of the sexual distinction of the generative 

 cells into * sperm-cells ' and ' germ-cells,' which we shall presently 

 see in the filamentous Confervacece, Conjugation between c two 

 adjacent cells of the same individual also occurs in some species. 



FIG. 420. Various stages of the history of a Spirogyra : A, three cells, a, b, c, of a 

 young filament, of which b is undergoing division ; B, two filaments in the first 

 stage of conjugation, showing the spiral disposition of their endochromes and the 

 protuberances from the conjugating cells ; C, completion of the act of conjugation, 

 the endochromes of the cells of the filament a having entirely passed over to those 

 of filament b, in which the zygospores are formed. 



Although the two conjugating filaments are nearly or quite morpho- 

 logically alike, there must clearly be a physiological differentiation, 

 since the conjugation takes place in one direction only. Where 

 conjugation occurs between cells in the same filament, this sexual 

 differentiation must be ascribed to the individual cells. Multipli- 

 cation by zoospores does not take place among the Conjugate. 



From the composite motile forms of Protococcus the transition 

 is easy to the group of Volvocineae, an assemblage of minute plants 

 of the greatest interest to the microscopist, on account both of the 

 animalcule -like activity of their movements and of the great beauty 

 and regularity of their, forms. The most remarkable example of this 

 group is the well-known Volvox globator (Plate VI), which is not 

 uncommon in fresh- water pools, and which, attaining a diameter of 

 about ^o or even 3^ of an inch, may be seen with the naked eye 

 when the drop containing it is held up to the light, swimming through 



