INTRODUCTION. 



case of the animal world, microscopic plants, irre- 

 spective of fructification, then, with a small cellular 

 alga, consisting of a single cell, 'Oi mm. in diameter, 

 or the one two thousand five hundredth part of an 

 inch as the lowest extreme, we shall have, in longi- 

 tudinal extension onl}-, the middle place occupied by 

 a small moss, such as Fiinaria hygrojuetrica, with a 

 total height of less than an inch-and-a-half. In 

 other words, the little moss would be as many times 

 higher than the one cell of the little green alga as 

 the tall tree of the Eucalyptus is higher than the 

 little moss. It would be difficult to calculate bulk 

 for bulk, and estimate size in all directions, so as 

 to ascertain how many such little cells as those of 

 the alga would be required to build up the trunk of 

 such a tree ; but the number would be enormous, 

 so far beyond human experience of numbers that 

 the mind would fail to appreciate their relationship. 

 The intermediate form is larger in plants than in 

 animals, because, although there are animals as 

 small as 'Oi mm., there are none reaching 420 feet 

 in height. 



Important as are the uses of plants to man, as the 

 source of food, clothing, and medicine, it has hardly 

 been considered as coming within the scope of this 

 volume to refer to them in this aspect, our object 

 being rather to present an accumulation of curious 

 and interesting facts in the structure, habits, or 



