BOTANICAL SUBJECTS. 155 



IX.—STEM AND RHIZOME. 



What is a stem ? Asa Gray says, " The stem is an ascending 

 axis seeking the light " ; while the " rhizome is a stem, which lies 

 on the ground, or is buried beneath its surface." There is really 

 no other distinction between the two than that of position. 



Asa Gray also states that " roots spring from the stem, not the 

 stem from the root." It would appear to me that it is neither the 

 one nor the other. Both are continuations of the same thing. 

 What is called the radicle in the embryo is a continuation of the 

 caulicle, and the prolongation below the cotyledons may be called 

 either a stem or a root. 



In " Bauer's Illustrations of Orchidaceous Plants," Lindley says 

 that when the tubercles of terrestrial orchids are deep in the earth, 

 they send up a root-like stem, which produces true roots, until it 

 reaches the light, and then develops leaves, such as Coryanthes 

 and others. 



Now, have we any means of getting at the genesis of the 

 rhizome } If we can do this, we have the origin of the stem, for 

 the latter is nothing but an upright rhizome. 



Dallinger in his " Minute forms of Life " has perhaps given 

 us a hint of the genesis of the rhizome in plants. He and Drys- 

 dale have watched, with great patience and perseverance, through 

 the microscope, the development of several monads, and have thus 

 given us their life-history. Fig. 39 shows us the various stages 

 in the process of multiplication of a monad by fission. At first 

 this monad is a simple cell with only one nucleus and a pair of 

 cilia. Then the nucleus becomes double as at (a), and the one 

 pair of cilia splits up in two separate pairs. The next steps are a 

 further separation of the nuclei with their cilia, as at {b) and (c). 

 Finally {d) shows us their condition before the separation into 

 two distinct unicellular bodies takes place. 



