152 UNIVERSITY OF MISSOURI BULLETIN 



Pleurococcus above referred to happens to be one of the 

 more common and widely distributed ones, and hence it is 

 called vulgaris. The plant was named by an early botanist, 

 Meneghini, and, according to botanical usage, the abbrevia- 

 tion of his name follows the specific name of the plant. 



Within the species no two individuals are precisely alike. 

 This is true whether the plant be a unicellular Pleurococcus, 

 or a myriad-celled oak tree. No two living things are ever 

 precisely alike. This is one of the most important and signi- 

 ficant facts about plants. But the individual variation is not 

 unlimited. It never departs from a given mean beyond a 

 maximum or a minimum extreme. This kind of variation is 

 known as fluctuating variation, and must be distinguished 

 from another type of variation in which some of the off- 

 spring of a given species of plant are found to fluctuate about 

 a different mean from that of the parent-plant. There is 

 not only qualitative change — a case of more or less in char- 

 acters already present — but a quantitative change, the ap- 

 pearance of an entirely new character. This is saltative 

 variation, variation by leaps, or mutation. 



But now the questions about Pleurococcus force them- 

 selves upon us- in endless number, and with peculiar fascina- 

 tion. How does the plant take in its nourishment from with- 

 out? How does it convert it into living protoplasm? What 

 are the waste products and how are they eliminated? What 

 is the significance of the green color, of the spherical shape, 

 the location on the north side of the tree, the existence of 

 the plant in North America? What is the method of inheri- 

 tance and the cause of variation? Why do some plants differ 

 from this one, and how did there come to be such a genus 

 as Pleurococcus, and such a species as Pleurococcus vulgaris^ 

 What is a plant, any way? What is life, and what does it 

 mean to be alive? How did life originate and what does it 

 mean to die? Such are only a few of the questions which 



