44 



BOTANT. 



56.— Cell-rormation 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, 

 Fig. 34.-Uiiioii (the however much it may resemble such a 

 of'the^Bwarm-spores'of purely physical process, the coalescing of 

 mf!"Ter^mayMZ the swarm-spores of the Myxomycetes is 

 Bith"oTwo°/warm^ Something more. It is possible that there 

 fused into one*^c three ^^ ^^° somc vcry slight difference between 



8wann spores ;' d, the the Uniting CClls. 

 same a few moments ■ ^ ■ 



afterward, the two up- 57. — In Cosmanum, a genus ox the 



peronesfusedintoom-. . . ° 



X 390.— After cienkow- Desmidiacess, 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. S&.—Cosmarlum Mmeghinil. a, b, e, different views of the mature plants ; 

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

 opment of the new cell. X 475.— After CErsted. 



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. 



