EXERCISE 93 

 REPRODUCTION IN SPIROGYRA 



Materials. Spirogyra reproduces freely in the spring or early 

 summer. Material should be collected at that time, examined, and, 

 if showing reproductive stages, should be preserved for use in the 

 laboratory when fresh material is not available. 



Directions for work. It is not usual to be able to find Spirogyra 

 in reproductive condition just when wanted. For that reason 

 you will be supplied with preserved material in bottles. Do not 

 remove more material than needed. 



When you have mounted a slide in the usual way, examine 

 it under the low power for reproductive stages (see textbook). 

 If you are quite confident that there is nothing of interest on 

 the slide, wipe the material off and prepare another promptly. 



Find and draw the following stages in the formation of the 

 spore : 



1. Protuberances from cells of two adjacent plants not yet 

 united. 



2. Protuberances united. 



3. Gamete passing through the tube. 



4. Completed spore. 



Draw stages in whatever order you find them, but label 

 properly and try to arrange in order. 



This method of spore formation by the union of two cells is 

 called sexual spore formation, or sexual reproduction. 



In this case is there any visible difference between the two 

 filaments, or the conjugating cells, corresponding to the male 

 and female sexes in higher "plants or animals ? When the spores 

 have been formed do you note any difference between the 

 filaments? Since each spore is a single cell, formed by the 

 union of two cells, how has the total number of cells changed? 

 Would the spores possess any advantage over the filaments if 

 the pond should dry up ? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 193, 194. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 224, 225. 



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