30 



PLANT STRUCTURES 



be solitary or several in a cell, and form very striking and 

 conspicuous objects (Figs. 13, 14). 



Spirogyra and its associates are further peculiar in pro- 

 ducing no asexual spores, and also in the method of sexual 

 reproduction. Two adjacent filaments put out tubular 

 processes toward one another. A cell of one filament sends 

 out a process which seeks to meet a corresponding process 

 from a cell of the other filament. When the tips of two 

 such processes come together, the end walls disappear, 



Fig. 15. Spirogyra, showing some common exceptions. At A two colls have been 

 connected by a tube, but without fusion a zygote has been organized in each cell; 

 also, the upper cell to the left has attempted to conjugate with the cell to the 

 right. At B there are cells from three filaments, the cells of the central one hav- 

 ing conjugated with both of the others.— Caldwell. 



and a continuous tube extending between the two cells is 

 organized (Figs. 14, 15). When many of the cells of two 

 parallel filaments become thus united, the appearance is 

 that of a ladder, with the filaments as the side pieces, and 

 the connecting tubes as the rounds. 



While the connecting tube is being developed the con- 

 tents of the two cells are organizing, and after the comple- 

 tion of the tube the contents of one cell pass through and 

 enter the other cell, fuse with its contents, and a sexual 



