8 MINUTE MARVELS OF NATURE 



other species of desmids which present a some- 

 what different method of reproduction. Instead 

 of breaking- away and subsequently acquiring a 

 complete shape, the two halves remain together, 

 but gradually develop at their line of junction, 

 two little rounded discs touching each other 

 at the edge, which gradually become larger and 

 push each other further apart, until, finally, the 

 indentations round the desmid's edges appear, 

 after which the two halves become detached as 

 perfect desmids. 



There are other and more complicated methods 

 of reproduction and cell division even with this same 

 Micrasterias ; but these need not concern us here, 

 though they show that even these lowly, single- 

 celled plants gradually approximate in structure 

 and methods of reproduction to higher and more 

 complicated forms. And it should also be ob- 

 served with regard to these delicate and beau- 

 tiful organisms, how frequently symmetry and 

 regularity of form prevail. But this we will 

 consider more in detail hereafter. 



Meanwhile let us glance at some of the most 

 extraordinary forms of the invisible vegetable 

 world — tiny unicellular plants of almost un- 

 imaginable minuteness, called " diatoms." 



These microscopic and wonderful algie are 

 abundantly distributed in nature. Wherever 



