RECORD OF LIFE IN THE ROCKS. 



165 



regard to the different ages of the earth's progress or 

 growth. 



249. Amphigens. The vegetable world presents to us 

 five groups, marked by different modes of growth. First 

 we have the amphigens, so named because they increase 

 by growth on all sides, the name being derived from two 

 Greek words, amphi, around, and gennao, to produce. 

 This mode of growth can be seen in the lichens that 

 spread out upon the surfaces of rocks, and trunks of 

 trees, and old fences. This division includes, besides 

 these lichens, tho scum-like growths that you see on 

 stagnant water (Conferva), the mushroom family (Fun- 

 gi), and the sea- weeds (Algae) that lie upon the shelves 

 and ledges of the shallow places in the sea. These are 

 all represented in Fig. 85. They nre the lowest kinds of 



Fig. 85. 



vegetation, and are found where no other plants can 

 grow. They may be considered as pioneers of the higher 

 orders of plants, helping to weather the rock, and to 

 gather upon it the material for the growth, in time, of 



