INTRODUCTION. 3 



partially decayed twig, half -buried in the earth in a 

 wood, we may find it completely covered with various 

 representatives of these different vegetable growths ; and 

 nothing surely can give us a more striking or convincing 

 proof of the universal diffusion of life. All these dif- 

 ferent plants belong to the second great division of the 

 vegetable kingdom, to which the name of cryptogamia 

 has been given, on account of the absence, in all the 

 members, of those prominent organs which are essential 

 to the production of perfect seed. They are propagated 

 by little embryo plants called spores or sporules, gene- 

 rally invisible to the naked eye, and differing from true 

 seeds in germinating from any part of their surface in- 

 stead of from two invariable points. Besides this grand 

 distinguishing mark, they possess several other peculiar 

 qualities in common. They consist of cells only, and 

 hence are often called cellular plants, in contradistinction 

 to those plants which are possessed of fibres and woody 

 tissue. Their development is also superficial, growth 

 taking place from the various terminal points ; and hence 

 they are called acrogens and thallogens, to distinguish 

 them from monocotyledonous and dicotyledonous plants. 

 Popularly, they are known as mosses, lichens, algae, and 

 fungi. They open up a vast field of physiological re- 

 search. They constitute a microcosm, an imperium in 

 imperio, a strange minute world underlying this great 

 world of sense and sight, which, though unseen and un- 

 heeded by man, is yet ever in full and active operation 

 around us. It is pleasant to turn aside for a while from 

 the busy human world, with its ceaseless anxieties, sor- 

 rows and labours, to avert our gaze from the splendours 



