8o 



Practical Plant Biology. 



individuals. The origin of both ova and sperms is similar to that 

 of the spores. Certain cells in the wall of the young individual 



FIG. 14. Volvox aureus. A, female sphere, x 80, showing nine ova ; B, two 

 adjacent somatic cells with protoplasmic connections; C, antheridium, 

 with packet of sperms ; D, sperms having broken loose from packet. 



enlarge. In the case of the ova this enlargement is accompanied 

 by a darkening or intensification of the green colour. This 



enlargement and darkening are 

 the only marked visible changes 

 unJergone by the cells which 

 are to become ova. In this 

 condition, enclosed in a cavity 

 of the cell-wall, they await fer- 

 tilisation. The enlarged cells 

 which give rise to the sperms 

 are lighter in colour. While 

 still enclosed in a cavity in the 

 wall of the sphere, they sub- 

 divide and produce a plate of 

 cells. The cells of this plate 

 further subdivide, always how- 

 ever at right angles to the sur- 



, 15. Volvox aureus, male 

 sphere, x 80, showing packets of 

 sperms in the antheridia. 



face of the plate, and thus form 

 a large number of narrow pris- 

 matic cells (32) lying parallel to each other like the faggots in a 

 bundle. These cells gradually become tapered towards one end 



