186 



STUDIES IN CRYPTOGAMS 



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

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

 341.) The chlorophyll is arranged in beautiful spiral bands near the 

 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. 340, by delicate strands of proto- 

 plasm radiating toward the wall and terminating 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 pro- 

 toplasm and nucleus cannot be easily seen, but if the 

 plant is stained with a dilute alcoholic solution of eosin 

 (153) 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 dor- 

 mant for a time, are formed by a process known as con- 

 jugation. Two threads lying side by side send out 

 short projections, usually from all the cells of a long 

 series. (Fig. 341.) The projections or processes from 

 opposite cells grow toward each other, meet and fuse, 

 forming a connecting tube between the cells. The 

 protoplasm, nucleus and chlorophyll band of one cell 

 now pass through this tube, and unite with the con- 

 tents of the other cell. The entire mass then becomes surrounded by 

 a thick cellulose wall, thus completing the resting-spore, or zygospore. 

 (Fig. 341, z.) 



Vaucheria is another alga common in shallow water and on damp 

 soil. The thallus is much branched, but the threads are not divided 

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

 colorless root-like organs which are much like the root-hairs of the 

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

 grains scattered through the thread. 



Vaucheria has a special mode of vegetative reproduction by means 

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

 6hort, enlarged lateral branch known as the sporangium. When the 

 sporangium bursts the entire contents escape, forming a single large 

 swarm-spore, which swims about by means of numerous lashes or cilia 

 on its surface. The swarm-spores are so large that they can be seen with 

 the naked eye. After swimming about for some time they come to 

 rest and germinate, producing a new plant, 



341. Conjugation 

 of spirogyra. 

 Ripe zygo- 

 spores on the 

 left ; connect- 

 ing a, tubes. 



