44 



BOTANY. 



56— Cell-Formation by TJnion. 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.-ui)ion (the howevBr much it may resemble such a 



so-called coEjugatlou) i i • i j.i i ■ j* 



of tne swann-epores of purely physical process, the coalescmg of 



■Sf't^tmiymfum the swarm-spores of the Myxomycetes is 



Bir^/!T"wo "swarm^ Something more. It is possible that there 



fuBeditito one'^c three ^^ ^^^° somc Very slight difference between 



swarm-Bpores ;' d, the the Uniting Cells. 

 same a few moments ° 



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



per ones fused into oni'. .^ .,. ,. ... in i n 



X 390. — After cienkow- Desmidiaccse, the unitmg 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. S5.—CosmaHnm MenegMnil. a, b, e, different views of the mature plants; 

 d, e, and/, three stages in the formation of the new cell ; ff. A, 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 upion of cells in Spirogyra is much like that of 

 Qosmarium, Here the cells are united into long filamenta, 



