ALG51 



170 



be used. The thread is divided into long cells by cross-walls which, 

 according to the species, are either straight or curiously folded (Fig. 

 314). The chlorophyll is arranged in beautiful spiral bands near 

 tin- wall of each cell. From the character of these bands the plant 

 takes its name. Each cell is provided with a nucleus 

 and other protoplasm. The nucleus is suspended near 

 the center of the cell, a, Fig. 313, by delicate strands 

 of protoplasm radiating toward the wall and terminat- 

 ing at certain points in the chlorophyll band, The 

 remainder of the protoplasm forms a thin layer lining 

 the wall. The interior of the cell is filled with 

 cell-sap. The protoplasm and nucleus cannot be 

 easily seen, but if the plant is stained with a dilute 

 alcoholic solution of eosin (146) they become clear. 



Spirogyra is propagated vegetatively by the break- 

 ing off of parts of the threads, which continue to grow 

 as new plants. Resting-spores, which may remain 

 dormant for a time, an- formed by a process known as 

 conjugation. Two threads lying Bide by side semi out 

 short projections, usually from all the cells of a long 

 series (Fig. 314). The projections or processes from :; ". ( '""J. U ~- 

 opposite cells grow toward each other, meet and fuse, Ripe zygospores 

 forming a connecting tube between the cells. The connecting 

 protoplasm, nucleus, and chlorophyll band of one cell tabes. 

 now pass through this tube, and unite with the contents of the other 

 cell. Tin- entire mass then becomes Burrounded by a thick cellulose 

 wall, thus completing the resting -spore, or eygospon I 31 1, e). 



Vaucheria is another alga common in shallow water and on damp 

 soil. Tin- thallus is much branched, bul the threads are not divided 

 by cross-walls as in spirogyra. The plants are attached bymeansof 

 colorless root like organs which are much like the root hairs .!' the 

 higher plants: these are rhi oids. The chlorophyll is in the form of 

 grains scattered through the thread. 



Vaucheria has a Bpecial mode of vegetative reproduction by means 

 of swimming Bpores or swarm-spores. These are formed Bingly in a 

 short, enlarged lateral branch known as the sporangium. When the 

 sporangium bursts the entire contents escape, forming b Bingle 

 Bwarm- spore, which swims about bj means of numerous lashes or oilia 

 mi its Burface. The swarm Bpores are bo large thai they oan !" Been 

 with the naked eye. After Bwimming aboul for sunn- tune they oome 

 to real and germinate, producing a new plant. 



The formation of resting Of \ ainheria is accompli 



