44 



BOTANY. 



56. Cell-Formation by Union. The simplest example 

 of cell-formation by the union of cells is found in the Myx- 

 omycetes. The swarm-spores which have been described as 

 multiplying by division (see p. 36) somewhat later begin 

 the opposite process of uniting. Two or 

 more approach one another and gradually 

 coalesce into a homogeneous protoplasmic 

 mass (Fig. 34). During the process the 

 nuclei disappear. The union, at first 

 sight, appears to be no more than a mere 

 running together of similar drops; but the 

 disappearance of the nuclei shows that, 

 however much it may resemble such a 

 purely physical process, the coalescing of 

 the swarm-spores of the Myxomycetes is 

 something more. It is possible that there 

 is also some very slight difference between 



swarm-spores ; </, the the Uniting Cells. 



same a few moments . , , ' 



afterward, the two up- 57. In Cosmamum, a genus oi the 



per ones fused into oni-. ,_ . . . ., ... -,-. -,, 



x390.-AfterCienkow- Desmidiacese, the uniting cells have well- 

 developed walls, and as a consequence the 

 process is somewhat different from what it is in the Myxo- 

 mycetes. The cells, which in this genus are two-lobed (Fig. 

 35), approach each other ; each sends out from its centre a 

 protuberance which meets the other (d) ; the thin walls 

 separating the cavities of the protuberances are absorbed, and 



Fig. 35.Cosmarlum Meneghinil. a, b, c, different views of the mature plants ; 

 d, e, and/, three stages in the formation of the new cell ; g, h, and i, the after-devel- 

 opment of the new cell. X 475. After ffirsted. 



the united protoplasmic masses form a round ball (e), which 

 soon becomes enclosed in its own proper coatings (/). 



58. The union of cells in Spirogyra is much like that of 

 Cosmarium. Here the cells are united into long filaments, 



